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

[Brad King via cfe-commits]

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@@ -204,6 +204,29 @@ void Flang::AddAArch64TargetArgs(const ArgList &Args,
   }
 }
 
+static void addVSDefines(const ToolChain &TC, const ArgList &Args,
+                         ArgStringList &CmdArgs) {
+
+  unsigned ver = 0;
+  const VersionTuple vt = TC.computeMSVCVersion(nullptr, Args);
+  ver = vt.getMajor() * 10000000 + vt.getMinor().value_or(0) * 100000 +
+        vt.getSubminor().value_or(0);
+  CmdArgs.push_back(Args.MakeArgString("-D_MSC_VER=" + Twine(ver / 100000)));
+  CmdArgs.push_back(Args.MakeArgString("-D_MSC_FULL_VER=" + Twine(ver)));
+
+  llvm::Triple triple = TC.getTriple();
+  if (triple.isAArch64()) {
+    CmdArgs.push_back("-D_M_ARM64=1");
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bradking wrote:

Does LLVM/Flang support the `_M_ARM64EC` ABI?

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