[Mono] Fix Mono Windows x86 build and runtime crash. (#74639)

Fix Mono Windows x86 build and runtime crash.

Trying to validate a fix on x86 Windows Mono crashed runtime with
stack overflow. After some investigation it turns out that Mono
Windows x86 have SIMD disabled, but S.P.C was still build with
System.Runtime.Intrinsics support and implementation of methods
like get_IsSupported is implemented as follow:

.method public hidebysig specialname static
        bool  get_IsSupported() cil managed
{
  // Code size       6 (0x6)
  .maxstack  8
  IL_0000:  call       bool System.Runtime.Intrinsics.X86.Popcnt::get_IsSupported()
  IL_0005:  ret
} // end of method Popcnt::get_IsSupported

causing a stack overflow when called at runtime.

Fix make sure we won't add support for System.Runtime.Intrinsics
in S.P.C for Mono Windows x86 builds.

There was also a warning in debugger-agent.c when building debug
that caused build to fail, including fix for that as well.

Author: lateralusX

src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems

@@ -16,6 +16,7 @@
     <SupportsArmIntrinsics Condition="'$(Platform)' == 'arm64'">true</SupportsArmIntrinsics>
     <SupportsWasmIntrinsics Condition="'$(Platform)' == 'wasm'">true</SupportsWasmIntrinsics>
     <SupportsX86Intrinsics Condition="'$(Platform)' == 'x64' or ('$(Platform)' == 'x86' and '$(TargetsUnix)' != 'true')">true</SupportsX86Intrinsics>
+    <SupportsX86Intrinsics Condition="'$(Platform)' == 'x86' and '$(TargetsWindows)' == 'true' and '$(FeatureMono)' == 'true'">false</SupportsX86Intrinsics>
     <ILLinkSharedDirectory>$(MSBuildThisFileDirectory)ILLink\</ILLinkSharedDirectory>
     <IsBigEndian Condition="'$(Platform)' == 's390x'">true</IsBigEndian>
     <Is64Bit Condition="'$(Platform)' == 'arm64' or '$(Platform)' == 'x64' or '$(Platform)' == 's390x' or '$(Platform)' == 'loongarch64' or '$(Platform)' == 'ppc64le'">true</Is64Bit>

src/mono/mono/component/debugger-agent.c

@@ -1039,7 +1039,7 @@ socket_transport_connect (const char *address)
 	MonoAddressEntry *rp;
 	SOCKET sfd = INVALID_SOCKET;
 	int s = 0, res;
-	char *host;
+	char *host = NULL;
 	int port;
 
 	MONO_REQ_GC_SAFE_MODE;