[clang] [Clang][Cygwin] Cygwin x86_64 should accept __stdcall (PR #158385)

[Tomohiro Kashiwada via cfe-commits]

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@@ -983,6 +983,7 @@ class LLVM_LIBRARY_VISIBILITY CygwinX86_64TargetInfo : public X86_64TargetInfo {
       : X86_64TargetInfo(Triple, Opts) {
     this->WCharType = TargetInfo::UnsignedShort;
     this->WIntType = TargetInfo::UnsignedInt;
+    this->UseMicrosoftManglingForC = true;
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kikairoya wrote:

Perhaps `UseMicrosoftManglingForC` for x86/x86_64 should split out into a new PR?

https://github.com/llvm/llvm-project/pull/158385