[clang] [clang] Add /Zc:__STDC__ flag to clang-cl (PR #68690)

[Aaron Ballman via cfe-commits]

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@@ -282,7 +282,7 @@ LANGOPT(HIPUseNewLaunchAPI, 1, 0, "Use new kernel launching API for HIP")
 LANGOPT(OffloadUniformBlock, 1, 0, "Assume that kernels are launched with uniform block sizes (default true for CUDA/HIP and false otherwise)")
 LANGOPT(HIPStdPar, 1, 0, "Enable Standard Parallel Algorithm Acceleration for HIP (experimental)")
 LANGOPT(HIPStdParInterposeAlloc, 1, 0, "Replace allocations / deallocations with HIP RT calls when Standard Parallel Algorithm Acceleration for HIP is enabled (Experimental)")
-
+LANGOPT(MSVCEnableStdcMacro , 1, 0, "define __STDC__ with -fms-compatability")
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AaronBallman wrote:

```suggestion
LANGOPT(MSVCEnableStdcMacro , 1, 0, "Define __STDC__ with '-fms-compatability'")
```

https://github.com/llvm/llvm-project/pull/68690