diff --git a/clang/include/clang/Basic/LangOptions.def b/clang/include/clang/Basic/LangOptions.def
index 653efd362c530..87e29c402f837 100644
--- a/clang/include/clang/Basic/LangOptions.def
+++ b/clang/include/clang/Basic/LangOptions.def
@@ -184,6 +184,7 @@ BENIGN_LANGOPT(HeinousExtensions , 1, 0, "extensions that we really don't like a
 LANGOPT(Modules           , 1, 0, "modules semantics")
 COMPATIBLE_LANGOPT(ModulesTS  , 1, 0, "C++ Modules TS syntax")
 COMPATIBLE_LANGOPT(CPlusPlusModules, 1, 0, "C++ modules syntax")
+LANGOPT(BuiltinHeadersInSystemModules, 1, 0, "builtin headers belong to system modules, and _Builtin_ modules are ignored for cstdlib headers")
 BENIGN_ENUM_LANGOPT(CompilingModule, CompilingModuleKind, 3, CMK_None,
                     "compiling a module interface")
 BENIGN_LANGOPT(CompilingPCH, 1, 0, "building a pch")
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index b05ffd493b4d8..321b3d8ea750f 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -2407,6 +2407,12 @@ defm modules : BoolFOption<"modules",
   LangOpts<"Modules">, Default<!strconcat(fmodules_ts.KeyPath, "||", fcxx_modules.KeyPath)>,
   PosFlag<SetTrue, [CC1Option], "Enable the 'modules' language feature">,
   NegFlag<SetFalse>, BothFlags<[NoXarchOption, CoreOption]>>;
+def fbuiltin_headers_in_system_modules : Flag <["-"], "fbuiltin-headers-in-system-modules">,
+  Group<f_Group>,
+  Flags<[NoXarchOption,CC1Option]>,
+  ShouldParseIf<fmodules.KeyPath>,
+  HelpText<"builtin headers belong to system modules, and _Builtin_ modules are ignored for cstdlib headers">,
+  MarshallingInfoFlag<LangOpts<"BuiltinHeadersInSystemModules">>;
 def fmodule_maps : Flag <["-"], "fmodule-maps">, Flags<[CoreOption]>, Alias<fimplicit_module_maps>;
 def fmodule_name_EQ : Joined<["-"], "fmodule-name=">, Group<f_Group>,
   Flags<[NoXarchOption,CC1Option,CoreOption]>, MetaVarName<"<name>">,
diff --git a/clang/include/clang/Lex/ModuleMap.h b/clang/include/clang/Lex/ModuleMap.h
index 90ac84d3a4cd9..178906a753b5f 100644
--- a/clang/include/clang/Lex/ModuleMap.h
+++ b/clang/include/clang/Lex/ModuleMap.h
@@ -427,7 +427,6 @@ class ModuleMap {
   }
 
   /// Is this a compiler builtin header?
-  static bool isBuiltinHeader(StringRef FileName);
   bool isBuiltinHeader(const FileEntry *File);
 
   /// Add a module map callback.
diff --git a/clang/lib/Driver/ToolChains/Darwin.cpp b/clang/lib/Driver/ToolChains/Darwin.cpp
index d0e61c213f9c1..83d6e8b665767 100644
--- a/clang/lib/Driver/ToolChains/Darwin.cpp
+++ b/clang/lib/Driver/ToolChains/Darwin.cpp
@@ -2984,6 +2984,58 @@ bool Darwin::isAlignedAllocationUnavailable() const {
   return TargetVersion < alignedAllocMinVersion(OS);
 }
 
+static bool sdkSupportsBuiltinModules(
+    const Darwin::DarwinPlatformKind &TargetPlatform,
+    const Darwin::DarwinEnvironmentKind &TargetEnvironment,
+    const Optional<DarwinSDKInfo> &SDKInfo) {
+  switch (TargetEnvironment) {
+  case Darwin::NativeEnvironment:
+  case Darwin::Simulator:
+  case Darwin::MacCatalyst:
+    // Standard xnu/Mach/Darwin based environments
+    // depend on the SDK version.
+    break;
+  default:
+    // All other environments support builtin modules from the start.
+    return true;
+  }
+
+  if (!SDKInfo)
+    // If there is no SDK info, assume this is building against a
+    // pre-SDK version of macOS (i.e. before Mac OS X 10.4). Those
+    // don't support modules anyway, but the headers definitely
+    // don't support builtin modules either. It might also be some
+    // kind of degenerate build environment, err on the side of
+    // the old behavior which is to not use builtin modules.
+    return false;
+
+  VersionTuple SDKVersion = SDKInfo->getVersion();
+  switch (TargetPlatform) {
+  // Existing SDKs added support for builtin modules in the fall
+  // 2024 major releases.
+  case Darwin::MacOS:
+    return SDKVersion >= VersionTuple(15U);
+  case Darwin::IPhoneOS:
+    switch (TargetEnvironment) {
+    case Darwin::MacCatalyst:
+      // Mac Catalyst uses `-target arm64-apple-ios18.0-macabi` so the platform
+      // is iOS, but it builds with the macOS SDK, so it's the macOS SDK version
+      // that's relevant.
+      return SDKVersion >= VersionTuple(15U);
+    default:
+      return SDKVersion >= VersionTuple(18U);
+    }
+  case Darwin::TvOS:
+    return SDKVersion >= VersionTuple(18U);
+  case Darwin::WatchOS:
+    return SDKVersion >= VersionTuple(11U);
+
+  // New SDKs support builtin modules from the start.
+  default:
+    return true;
+  }
+}
+
 void Darwin::addClangTargetOptions(const llvm::opt::ArgList &DriverArgs,
                                    llvm::opt::ArgStringList &CC1Args,
                                    Action::OffloadKind DeviceOffloadKind) const {
@@ -3055,6 +3107,20 @@ void Darwin::addClangTargetOptions(const llvm::opt::ArgList &DriverArgs,
           options::OPT_fvisibility_inlines_hidden_static_local_var,
           options::OPT_fno_visibility_inlines_hidden_static_local_var))
     CC1Args.push_back("-fvisibility-inlines-hidden-static-local-var");
+
+  // Earlier versions of the darwin SDK have the C standard library headers
+  // all together in the Darwin module. That leads to module cycles with
+  // the _Builtin_ modules. e.g. <inttypes.h> on darwin includes <stdint.h>.
+  // The builtin <stdint.h> include-nexts <stdint.h>. When both of those
+  // darwin headers are in the Darwin module, there's a module cycle Darwin ->
+  // _Builtin_stdint -> Darwin (i.e. inttypes.h (darwin) -> stdint.h (builtin) ->
+  // stdint.h (darwin)). This is fixed in later versions of the darwin SDK,
+  // but until then, the builtin headers need to join the system modules.
+  // i.e. when the builtin stdint.h is in the Darwin module too, the cycle
+  // goes away. Note that -fbuiltin-headers-in-system-modules does nothing
+  // to fix the same problem with C++ headers, and is generally fragile.
+  if (!sdkSupportsBuiltinModules(TargetPlatform, TargetEnvironment, SDKInfo))
+    CC1Args.push_back("-fbuiltin-headers-in-system-modules");
 }
 
 DerivedArgList *
diff --git a/clang/lib/Lex/ModuleMap.cpp b/clang/lib/Lex/ModuleMap.cpp
index 5e67c6901bdd9..665bb94a66f23 100644
--- a/clang/lib/Lex/ModuleMap.cpp
+++ b/clang/lib/Lex/ModuleMap.cpp
@@ -253,6 +253,45 @@ Optional<FileEntryRef> ModuleMap::findHeader(
   return NormalHdrFile;
 }
 
+/// Determine whether the given file name is the name of a builtin
+/// header, supplied by Clang to replace, override, or augment existing system
+/// headers.
+static bool isBuiltinHeaderName(StringRef FileName) {
+  return llvm::StringSwitch<bool>(FileName)
+           .Case("float.h", true)
+           .Case("iso646.h", true)
+           .Case("limits.h", true)
+           .Case("stdalign.h", true)
+           .Case("stdarg.h", true)
+           .Case("stdatomic.h", true)
+           .Case("stdbool.h", true)
+           .Case("stddef.h", true)
+           .Case("stdint.h", true)
+           .Case("tgmath.h", true)
+           .Case("unwind.h", true)
+           .Default(false);
+}
+
+/// Determine whether the given module name is the name of a builtin
+/// module that is cyclic with a system module  on some platforms.
+static bool isBuiltInModuleName(StringRef ModuleName) {
+  return llvm::StringSwitch<bool>(ModuleName)
+           .Case("_Builtin_float", true)
+           .Case("_Builtin_inttypes", true)
+           .Case("_Builtin_iso646", true)
+           .Case("_Builtin_limits", true)
+           .Case("_Builtin_stdalign", true)
+           .Case("_Builtin_stdarg", true)
+           .Case("_Builtin_stdatomic", true)
+           .Case("_Builtin_stdbool", true)
+           .Case("_Builtin_stddef", true)
+           .Case("_Builtin_stdint", true)
+           .Case("_Builtin_stdnoreturn", true)
+           .Case("_Builtin_tgmath", true)
+           .Case("_Builtin_unwind", true)
+           .Default(false);
+}
+
 void ModuleMap::resolveHeader(Module *Mod,
                               const Module::UnresolvedHeaderDirective &Header,
                               bool &NeedsFramework) {
@@ -296,7 +335,7 @@ bool ModuleMap::resolveAsBuiltinHeader(
       llvm::sys::path::is_absolute(Header.FileName) ||
       Mod->isPartOfFramework() || !Mod->IsSystem || Header.IsUmbrella ||
       !BuiltinIncludeDir || BuiltinIncludeDir == Mod->Directory ||
-      !isBuiltinHeader(Header.FileName))
+      !LangOpts.BuiltinHeadersInSystemModules || !isBuiltinHeaderName(Header.FileName))
     return false;
 
   // This is a system module with a top-level header. This header
@@ -372,28 +411,9 @@ static StringRef sanitizeFilenameAsIdentifier(StringRef Name,
   return Name;
 }
 
-/// Determine whether the given file name is the name of a builtin
-/// header, supplied by Clang to replace, override, or augment existing system
-/// headers.
-bool ModuleMap::isBuiltinHeader(StringRef FileName) {
-  return llvm::StringSwitch<bool>(FileName)
-           .Case("float.h", true)
-           .Case("iso646.h", true)
-           .Case("limits.h", true)
-           .Case("stdalign.h", true)
-           .Case("stdarg.h", true)
-           .Case("stdatomic.h", true)
-           .Case("stdbool.h", true)
-           .Case("stddef.h", true)
-           .Case("stdint.h", true)
-           .Case("tgmath.h", true)
-           .Case("unwind.h", true)
-           .Default(false);
-}
-
 bool ModuleMap::isBuiltinHeader(const FileEntry *File) {
-  return File->getDir() == BuiltinIncludeDir &&
-         ModuleMap::isBuiltinHeader(llvm::sys::path::filename(File->getName()));
+  return File->getDir() == BuiltinIncludeDir && LangOpts.BuiltinHeadersInSystemModules &&
+         isBuiltinHeaderName(llvm::sys::path::filename(File->getName()));
 }
 
 ModuleMap::HeadersMap::iterator
@@ -2513,7 +2533,10 @@ void ModuleMapParser::parseHeaderDecl(MMToken::TokenKind LeadingToken,
   }
 
   bool NeedsFramework = false;
-  Map.addUnresolvedHeader(ActiveModule, std::move(Header), NeedsFramework);
+  // Don't add the top level headers to the builtin modules if the builtin headers
+  // belong to the system modules.
+  if (!Map.LangOpts.BuiltinHeadersInSystemModules || ActiveModule->isSubModule() || !isBuiltInModuleName(ActiveModule->Name))
+    Map.addUnresolvedHeader(ActiveModule, std::move(Header), NeedsFramework);
 
   if (NeedsFramework && ActiveModule)
     Diags.Report(CurrModuleDeclLoc, diag::note_mmap_add_framework_keyword)
diff --git a/clang/test/Driver/Inputs/DriverKit23.0.sdk/SDKSettings.json b/clang/test/Driver/Inputs/DriverKit23.0.sdk/SDKSettings.json
new file mode 100644
index 0000000000000..7ba6c244df211
--- /dev/null
+++ b/clang/test/Driver/Inputs/DriverKit23.0.sdk/SDKSettings.json
@@ -0,0 +1 @@
+{"Version":"23.0", "MaximumDeploymentTarget": "23.0.99"}
diff --git a/clang/test/Driver/Inputs/MacOSX15.0.sdk/SDKSettings.json b/clang/test/Driver/Inputs/MacOSX15.0.sdk/SDKSettings.json
new file mode 100644
index 0000000000000..77b70e1a83c19
--- /dev/null
+++ b/clang/test/Driver/Inputs/MacOSX15.0.sdk/SDKSettings.json
@@ -0,0 +1 @@
+{"Version":"990.0", "MaximumDeploymentTarget": "99.0.99"}
diff --git a/clang/test/Driver/Inputs/MacOSX15.1.sdk/SDKSettings.json b/clang/test/Driver/Inputs/MacOSX15.1.sdk/SDKSettings.json
new file mode 100644
index 0000000000000..d46295b2ab5a1
--- /dev/null
+++ b/clang/test/Driver/Inputs/MacOSX15.1.sdk/SDKSettings.json
@@ -0,0 +1 @@
+{"Version":"15.1", "MaximumDeploymentTarget": "15.1.99"}
diff --git a/clang/test/Driver/darwin-builtin-modules.c b/clang/test/Driver/darwin-builtin-modules.c
new file mode 100644
index 0000000000000..4564d7317d7ab
--- /dev/null
+++ b/clang/test/Driver/darwin-builtin-modules.c
@@ -0,0 +1,15 @@
+// Check that darwin passes -fbuiltin-headers-in-system-modules
+// when expected.
+
+// RUN: %clang -target x86_64-apple-darwin22.4 -### %s 2>&1 | FileCheck %s
+// RUN: %clang -isysroot %S/Inputs/MacOSX10.15.versioned.sdk -target x86_64-apple-macos10.15 -### %s 2>&1 | FileCheck %s
+// RUN: %clang -isysroot %S/Inputs/iPhoneOS13.0.sdk -target arm64-apple-ios13.0 -### %s 2>&1 | FileCheck %s
+// CHECK: -fbuiltin-headers-in-system-modules
+
+// RUN: %clang -isysroot %S/Inputs/MacOSX15.0.sdk -target x86_64-apple-macos14.0 -### %s 2>&1 | FileCheck --check-prefix=CHECK_FUTURE %s
+// RUN: %clang -isysroot %S/Inputs/MacOSX15.0.sdk -target x86_64-apple-macos15.0 -### %s 2>&1 | FileCheck --check-prefix=CHECK_FUTURE %s
+// RUN: %clang -isysroot %S/Inputs/MacOSX15.0.sdk -target x86_64-apple-ios18.0-macabi -### %s 2>&1 | FileCheck --check-prefix=CHECK_FUTURE %s
+// RUN: %clang -isysroot %S/Inputs/MacOSX15.1.sdk -target x86_64-apple-macos15.1 -darwin-target-variant x86_64-apple-ios18.1-macabi -### %s 2>&1 | FileCheck --check-prefix=CHECK_FUTURE %s
+// RUN: %clang -isysroot %S/Inputs/MacOSX15.1.sdk -target x86_64-apple-ios18.1-macabi -darwin-target-variant x86_64-apple-macos15.1 -### %s 2>&1 | FileCheck --check-prefix=CHECK_FUTURE %s
+// RUN: %clang -isysroot %S/Inputs/DriverKit23.0.sdk -target arm64-apple-driverkit23.0 -### %s 2>&1 | FileCheck --check-prefix=CHECK_FUTURE %s
+// CHECK_FUTURE-NOT: -fbuiltin-headers-in-system-modules
diff --git a/clang/test/Modules/Werror-Wsystem-headers.m b/clang/test/Modules/Werror-Wsystem-headers.m
index 164c5b2ab672a..44633ef430b99 100644
--- a/clang/test/Modules/Werror-Wsystem-headers.m
+++ b/clang/test/Modules/Werror-Wsystem-headers.m
@@ -3,19 +3,21 @@
 // RUN: mkdir %t-saved
 
 // Initial module build
-// RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -fdisable-module-hash \
-// RUN:     -isystem %S/Inputs/System/usr/include -fsyntax-only %s -verify
+// RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fbuiltin-headers-in-system-modules \
+// RUN:     -fmodules-cache-path=%t -fdisable-module-hash -isystem %S/Inputs/System/usr/include \
+// RUN:     -fsyntax-only %s -verify
 // RUN: cp %t/cstd.pcm %t-saved/cstd.pcm
 
 // Even with -Werror don't rebuild a system module
-// RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -fdisable-module-hash \
-// RUN:     -isystem %S/Inputs/System/usr/include -fsyntax-only %s -verify -Werror
+// RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fbuiltin-headers-in-system-modules \
+// RUN:     -fmodules-cache-path=%t -fdisable-module-hash -isystem %S/Inputs/System/usr/include \
+// RUN:     -fsyntax-only %s -verify -Werror
 // RUN: diff %t/cstd.pcm %t-saved/cstd.pcm
 
 // Unless -Wsystem-headers is on
-// RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -fdisable-module-hash \
-// RUN:     -isystem %S/Inputs/System/usr/include -fsyntax-only %s -verify \
-// RUN:     -Werror=unused -Wsystem-headers
+// RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fbuiltin-headers-in-system-modules \
+// RUN:     -fmodules-cache-path=%t -fdisable-module-hash -isystem %S/Inputs/System/usr/include \
+// RUN:     -fsyntax-only %s -verify -Werror=unused -Wsystem-headers
 // RUN: not diff %t/cstd.pcm %t-saved/cstd.pcm
 
 // expected-no-diagnostics
diff --git a/clang/test/Modules/context-hash.c b/clang/test/Modules/context-hash.c
index 8bb7422f6a54f..de3303a9b0b64 100644
--- a/clang/test/Modules/context-hash.c
+++ b/clang/test/Modules/context-hash.c
@@ -4,22 +4,24 @@
 // RUN: rm -rf %t
 // RUN: %clang_cc1 -fsyntax-only -internal-isystem \
 // RUN:   %S/Inputs/System/usr/include -fmodules -fimplicit-module-maps \
-// RUN:   -fmodules-cache-path=%t %s -Rmodule-build 2> %t1
+// RUN:   -fbuiltin-headers-in-system-modules -fmodules-cache-path=%t %s \
+// RUN:   -Rmodule-build 2> %t1
 // RUN: rm -rf %t
 // RUN: %clang_cc1 -fsyntax-only -internal-isystem \
 // RUN:   %S/Inputs/System/usr/include -internal-isystem %S -fmodules \
-// RUN:   -fimplicit-module-maps -fmodules-cache-path=%t %s -Rmodule-build 2> \
-// RUN:   %t2
+// RUN:   -fbuiltin-headers-in-system-modules -fimplicit-module-maps \
+// RUN:   -fmodules-cache-path=%t %s -Rmodule-build 2> %t2
 // RUN: rm -rf %t
 // RUN: %clang_cc1 -fsyntax-only -internal-isystem \
 // RUN:   %S/Inputs/System/usr/include -internal-isystem %S -fmodules \
-// RUN:   -fimplicit-module-maps -fmodules-cache-path=%t %s \
-// RUN:   -fmodules-strict-context-hash -Rmodule-build 2> %t3
+// RUN:   -fbuiltin-headers-in-system-modules -fimplicit-module-maps \
+// RUN:   -fmodules-cache-path=%t %s -fmodules-strict-context-hash \
+// RUN:   -Rmodule-build 2> %t3
 // RUN: rm -rf %t
 // RUN: %clang_cc1 -fsyntax-only -Weverything -internal-isystem \
 // RUN:   %S/Inputs/System/usr/include -fmodules -fmodules-strict-context-hash \
-// RUN:   -fimplicit-module-maps -fmodules-cache-path=%t %s -Rmodule-build 2> \
-// RUN:   %t4
+// RUN:   -fbuiltin-headers-in-system-modules -fimplicit-module-maps \
+// RUN:   -fmodules-cache-path=%t %s -Rmodule-build 2> %t4
 // RUN: echo %t > %t.path
 // RUN: cat %t.path %t1 %t2 %t3 %t4 | FileCheck %s
 
@@ -29,16 +31,17 @@
 // RUN: rm -rf %t
 // RUN: %clang_cc1 -fsyntax-only -internal-isystem \
 // RUN:   %S/Inputs/System/usr/include -fmodules -fimplicit-module-maps \
-// RUN:   -fmodules-cache-path=%t -x objective-c %s -Rmodule-build 2> %t1
+// RUN:   -fbuiltin-headers-in-system-modules -fmodules-cache-path=%t \
+// RUN:   -x objective-c %s -Rmodule-build 2> %t1
 // RUN: rm -rf %t
 // RUN: %clang_cc1 -fsyntax-only -internal-isystem \
 // RUN:   %S/Inputs/System/usr/include -fmodules -fimplicit-module-maps \
-// RUN:   -fobjc-runtime=macosx-1.0.0.0 \
+// RUN:   -fbuiltin-headers-in-system-modules -fobjc-runtime=macosx-1.0.0.0 \
 // RUN:   -fmodules-cache-path=%t -x objective-c %s -Rmodule-build 2> %t2
 // RUN: rm -rf %t
 // RUN: %clang_cc1 -fsyntax-only -internal-isystem \
 // RUN:   %S/Inputs/System/usr/include -fmodules -fimplicit-module-maps \
-// RUN:   -fcomment-block-commands=lp,bj \
+// RUN:   -fbuiltin-headers-in-system-modules -fcomment-block-commands=lp,bj \
 // RUN:   -fmodules-cache-path=%t -x objective-c %s -Rmodule-build 2> %t3
 // RUN: echo %t > %t.path
 // RUN: cat %t.path %t1 %t2 %t3 | FileCheck --check-prefix=LANGOPTS %s
diff --git a/clang/test/Modules/crash-vfs-include-pch.m b/clang/test/Modules/crash-vfs-include-pch.m
index 5289f184eb04c..4c05a07d0f74d 100644
--- a/clang/test/Modules/crash-vfs-include-pch.m
+++ b/clang/test/Modules/crash-vfs-include-pch.m
@@ -5,14 +5,14 @@
 
 // RUN: %clang_cc1 -x objective-c-header -emit-pch %S/Inputs/pch-used.h \
 // RUN:     -o %t/out/pch-used.h.pch -fmodules -fimplicit-module-maps \
-// RUN:     -fmodules-cache-path=%t/cache -O0 \
+// RUN:     -fbuiltin-headers-in-system-modules -fmodules-cache-path=%t/cache -O0 \
 // RUN:     -isystem %S/Inputs/System/usr/include
 
 // RUN: env FORCE_CLANG_DIAGNOSTICS_CRASH= TMPDIR=%t TEMP=%t TMP=%t \
 // RUN: not %clang %s -E -include-pch %t/out/pch-used.h.pch -fmodules -nostdlibinc \
-// RUN:     -fimplicit-module-maps -fmodules-cache-path=%t/cache -O0 \
-// RUN:     -Xclang -fno-validate-pch -isystem %S/Inputs/System/usr/include \
-// RUN:     -o %t/output.E 2>&1 | FileCheck %s
+// RUN:     -fimplicit-module-maps -fbuiltin-headers-in-system-modules \
+// RUN:     -fmodules-cache-path=%t/cache -O0 -Xclang -fno-validate-pch \
+// RUN:     -isystem %S/Inputs/System/usr/include -o %t/output.E 2>&1 | FileCheck %s
 
 // RUN: FileCheck --check-prefix=CHECKSH %s -input-file %t/crash-vfs-*.sh
 // RUN: FileCheck --check-prefix=CHECKYAML %s -input-file \
diff --git a/clang/test/Modules/cstd.m b/clang/test/Modules/cstd.m
index f07ad85ec5126..6b81b9013e9da 100644
--- a/clang/test/Modules/cstd.m
+++ b/clang/test/Modules/cstd.m
@@ -1,5 +1,5 @@
 // RUN: rm -rf %t
-// RUN: %clang_cc1 -fsyntax-only -internal-isystem %S/Inputs/System/usr/include -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -D__need_wint_t -Werror=implicit-function-declaration %s
+// RUN: %clang_cc1 -fsyntax-only -internal-isystem %S/Inputs/System/usr/include -fmodules -fimplicit-module-maps -fbuiltin-headers-in-system-modules -fmodules-cache-path=%t -D__need_wint_t -Werror=implicit-function-declaration %s
 
 @import uses_other_constants;
 const double other_value = DBL_MAX;
diff --git a/clang/test/Modules/pch-used.m b/clang/test/Modules/pch-used.m
index 31d358391ce7f..5f6ffec337a51 100644
--- a/clang/test/Modules/pch-used.m
+++ b/clang/test/Modules/pch-used.m
@@ -1,8 +1,8 @@
 // UNSUPPORTED: -zos, -aix
 // RUN: rm -rf %t
 // RUN: mkdir %t
-// RUN: %clang_cc1 -x objective-c-header -emit-pch %S/Inputs/pch-used.h -o %t/pch-used.h.pch -fmodules -fimplicit-module-maps -fmodules-cache-path=%t/cache -O0 -isystem %S/Inputs/System/usr/include
-// RUN: %clang_cc1 %s -include-pch %t/pch-used.h.pch -fmodules -fimplicit-module-maps -fmodules-cache-path=%t/cache -O0 -isystem %S/Inputs/System/usr/include -emit-llvm -o - | FileCheck %s
+// RUN: %clang_cc1 -x objective-c-header -emit-pch %S/Inputs/pch-used.h -o %t/pch-used.h.pch -fmodules -fimplicit-module-maps -fbuiltin-headers-in-system-modules -fmodules-cache-path=%t/cache -O0 -isystem %S/Inputs/System/usr/include
+// RUN: %clang_cc1 %s -include-pch %t/pch-used.h.pch -fmodules -fimplicit-module-maps -fbuiltin-headers-in-system-modules -fmodules-cache-path=%t/cache -O0 -isystem %S/Inputs/System/usr/include -emit-llvm -o - | FileCheck %s
 
 void f(void) { SPXTrace(); }
 void g(void) { double x = DBL_MAX; }
diff --git a/clang/test/Modules/shadowed-submodule.m b/clang/test/Modules/shadowed-submodule.m
index c9c77bd13a1ca..6f34303d953e2 100644
--- a/clang/test/Modules/shadowed-submodule.m
+++ b/clang/test/Modules/shadowed-submodule.m
@@ -1,5 +1,5 @@
 // RUN: rm -rf %t
-// RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -I %S/Inputs/shadowed-submodule/Foo -I %S/Inputs/shadowed-submodule/A2 %s -verify
+// RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fbuiltin-headers-in-system-modules -fmodules-cache-path=%t -I %S/Inputs/shadowed-submodule/Foo -I %S/Inputs/shadowed-submodule/A2 %s -verify
 
 @import Foo; // expected-error {{module 'A' was built in directory}}
              // expected-note@shadowed-submodule.m:4 {{imported by module 'Foo'}}
diff --git a/clang/test/Modules/stddef.c b/clang/test/Modules/stddef.c
index c33f3643112bb..c164964c6ffa3 100644
--- a/clang/test/Modules/stddef.c
+++ b/clang/test/Modules/stddef.c
@@ -1,5 +1,5 @@
 // RUN: rm -rf %t
-// RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -I%S/Inputs/StdDef %s -verify -fno-modules-error-recovery
+// RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fbuiltin-headers-in-system-modules -fmodules-cache-path=%t -I%S/Inputs/StdDef %s -verify -fno-modules-error-recovery
 
 #include "ptrdiff_t.h"
 
diff --git a/clang/test/Modules/stddef.m b/clang/test/Modules/stddef.m
index 4f2d6bb7407b3..1ff6ff73796ab 100644
--- a/clang/test/Modules/stddef.m
+++ b/clang/test/Modules/stddef.m
@@ -3,5 +3,5 @@
 size_t getSize(void);
 
 // RUN: rm -rf %t
-// RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -I %S/Inputs/StdDef %s -verify
+// RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fbuiltin-headers-in-system-modules -fmodules-cache-path=%t -I %S/Inputs/StdDef %s -verify
 // expected-no-diagnostics