[flang] [clang] [flang] Add MSC_VER and target arch defines when targeting the MSVC ABI (PR #73250)

[Brad King via cfe-commits]

================
@@ -322,6 +345,7 @@ void Flang::addTargetOptions(const ArgList &Args,
 
   if (Triple.isKnownWindowsMSVCEnvironment()) {
     processVSRuntimeLibrary(TC, Args, CmdArgs);
+    addVSDefines(TC, Args, CmdArgs);
   }
 
   // TODO: Add target specific flags, ABI, mtune option etc.
----------------
bradking wrote:

Please also add `-D_WIN32` to indicate that this is targeting a Windows platform.


https://github.com/llvm/llvm-project/pull/73250