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

[Andrzej Warzyński 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,
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banach-space wrote:

```suggestion
static void addMSVCDefines(const ToolChain &TC, const ArgList &Args,
```
?

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