[flang] [llvm] [flang] improve compatibility with mingw headers (PR #172041)

[Eugene Epshteyn via llvm-commits]

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@@ -23,11 +23,9 @@
 #define unlink _unlink
 #define PATH_MAX MAX_PATH
 
-#ifdef _MSC_VER
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eugeneepshteyn wrote:

Maybe it should be something like `#if defined(_MSC_VER) || defined(__MINGW32__)` ?  Or is process/thread API is standard among all possible Windows compilers?

https://github.com/llvm/llvm-project/pull/172041