macOS link + libco MSVC: drop librt on Apple, shim libco TLS

macOS link failed with "ld: library 'rt' not found": librt is glibc-only
(clock_gettime etc. live in libSystem on macOS). The uv/libgit2/libmdbx
consumer stubs linked rt in their non-Windows branch, which also caught
macOS — gate rt on Linux only (NOT WIN32 AND NOT APPLE).

libco Windows: /std:c17 did not make MSVC define __STDC__, so libco's
thread_local/alignas stayed undefined under LIBCO_MP. Force-include a
shim (/FI) that defines both via __declspec before settings.h, which
libco honours through its #if !defined(...) guards.

Author: zokrezyl

build-tools/3rdparty/libco/_build.sh

@@ -101,13 +101,22 @@ windows-x86_64)
         echo "windows-x86_64 requires MSVC cl on PATH (run vcvarsall x64)" >&2; exit 1; }
     CC=cl
     AR=lib
-    # /std:c17 makes MSVC define __STDC__, which gates libco settings.h's
-    # _MSC_VER branch that maps thread_local -> __declspec(thread) and
-    # alignas -> __declspec(align(...)). Without it neither the C nor C++
-    # branch is taken and `thread_local`/`alignas` stay undefined keywords,
-    # so amd64.c fails to compile under LIBCO_MP.
-    CFLAGS_BASE="/nologo /O2 /MD /std:c17 /DLIBCO_MP /D_CRT_SECURE_NO_WARNINGS"
+    CFLAGS_BASE="/nologo /O2 /MD /DLIBCO_MP /D_CRT_SECURE_NO_WARNINGS"
     CFLAGS_EXTRA=""
+    # Under MSVC C mode __STDC__ is undefined, so libco settings.h leaves
+    # `thread_local` and `alignas` undefined (its mapping to __declspec(...)
+    # is gated on __STDC__/_cplusplus). amd64.c then fails to compile under
+    # LIBCO_MP. libco honours a user-provided definition (#if !defined(...)),
+    # so force-include a shim that defines both before settings.h is reached.
+    LIBCO_MSVC_SHIM="$WORK_DIR/picomesh-libco-msvc-shim.h"
+    cat > "$LIBCO_MSVC_SHIM" <<'SHIM'
+#ifndef thread_local
+#define thread_local __declspec(thread)
+#endif
+#ifndef alignas
+#define alignas(bytes) __declspec(align(bytes))
+#endif
+SHIM
     ;;
 *)
     echo "unknown TARGET_PLATFORM: $TARGET_PLATFORM" >&2
@@ -125,7 +134,8 @@ if [ "$TARGET_PLATFORM" = "windows-x86_64" ]; then
     _OBJ_W=$(cygpath -w "$WORK_DIR/libco.obj")
     _OUT_W=$(cygpath -w "$INSTALL_DIR/lib/libco.lib")
     _SRC_DIR_W=$(cygpath -w "$SRC_DIR")
-    MSYS2_ARG_CONV_EXCL='*' $CC $CFLAGS "/I${_SRC_DIR_W}" /c "$_SRC_W" "/Fo${_OBJ_W}"
+    _SHIM_W=$(cygpath -w "$LIBCO_MSVC_SHIM")
+    MSYS2_ARG_CONV_EXCL='*' $CC $CFLAGS "/FI${_SHIM_W}" "/I${_SRC_DIR_W}" /c "$_SRC_W" "/Fo${_OBJ_W}"
     MSYS2_ARG_CONV_EXCL='*' $AR /nologo "/OUT:${_OUT_W}" "${_OBJ_W}"
 else
     $CC $CFLAGS -I"$SRC_DIR" -c "$SRC_DIR/libco.c" -o "$WORK_DIR/libco.o"

build-tools/picomesh/libs/libgit2.cmake

@@ -40,7 +40,10 @@ if(WIN32)
     target_link_libraries(libgit2 INTERFACE zlib-ng
         ws2_32 advapi32 rpcrt4 crypt32 ole32 secur32 winhttp)
 else()
-    target_link_libraries(libgit2 INTERFACE zlib-ng Threads::Threads rt)
+    target_link_libraries(libgit2 INTERFACE zlib-ng Threads::Threads)
+    if(NOT APPLE)
+        target_link_libraries(libgit2 INTERFACE rt)  # glibc clock_gettime; not on macOS
+    endif()
 endif()
 
 message(STATUS "libgit2: prebuilt v${PICOMESH_3RDPARTY_libgit2_VERSION} (${_LG_LIB})")

build-tools/picomesh/libs/libmdbx.cmake

@@ -32,7 +32,10 @@ find_package(Threads REQUIRED)
 if(WIN32)
     target_link_libraries(libmdbx INTERFACE ntdll advapi32 user32 kernel32)
 else()
-    target_link_libraries(libmdbx INTERFACE Threads::Threads rt)
+    target_link_libraries(libmdbx INTERFACE Threads::Threads)
+    if(NOT APPLE)
+        target_link_libraries(libmdbx INTERFACE rt)  # glibc clock_gettime; not on macOS
+    endif()
 endif()
 
 message(STATUS "libmdbx: prebuilt v${PICOMESH_3RDPARTY_libmdbx_VERSION} (${_LM_LIB})")

build-tools/picomesh/libs/uv.cmake

@@ -30,14 +30,18 @@ set_target_properties(uv PROPERTIES
     IMPORTED_LOCATION             "${_LIBUV_LIB}"
     INTERFACE_INCLUDE_DIRECTORIES "${_LIBUV_DIR}/include"
 )
-# libuv's transitive system deps differ by platform: POSIX needs libm/librt +
-# dl; native Windows needs the Win32 socket/process/debug libraries instead
-# (m/rt do not exist there).
+# libuv's transitive system deps differ by platform: native Windows needs the
+# Win32 socket/process/debug libraries; POSIX needs libm + dl. librt (clock_*)
+# is glibc-only — it does NOT exist on macOS (those live in libSystem), so add
+# it on Linux only.
 if(WIN32)
     target_link_libraries(uv INTERFACE
         ws2_32 iphlpapi psapi userenv dbghelp ole32 shell32 advapi32)
 else()
-    target_link_libraries(uv INTERFACE Threads::Threads ${CMAKE_DL_LIBS} m rt)
+    target_link_libraries(uv INTERFACE Threads::Threads ${CMAKE_DL_LIBS} m)
+    if(NOT APPLE)
+        target_link_libraries(uv INTERFACE rt)
+    endif()
 endif()
 
 message(STATUS "libuv: prebuilt @${PICOMESH_3RDPARTY_libuv_VERSION} (${_LIBUV_LIB})")