[clang] [clang][MinGW] Implement -mcrtdll option to switch crt choice (PR #149469)

[Martin Storsjö via cfe-commits]

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@@ -493,6 +493,9 @@ LANGOPT(BoundsSafety, 1, 0, NotCompatible, "Bounds safety extension for C")
 
 LANGOPT(PreserveVec3Type, 1, 0, NotCompatible, "Preserve 3-component vector type")
 
+ENUM_LANGOPT(MinGWCRTDll, WindowsCRTDLLVersion, 4, WindowsCRTDLLVersion::CRTDLL_Default, NotCompatible,
+             "MinGW specific. Controls the __MSVCRT_VERSION and related preprocessor defines.")
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mstorsjo wrote:

Typo, `__MSVCRT_VERSION__` with two trailing underscores.

https://github.com/llvm/llvm-project/pull/149469