[clang] [clang] UEFI ABI fixes for X86_64 (PR #124992)

[Roland McGrath via cfe-commits]

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@@ -5193,12 +5193,12 @@ bool Sema::CheckCallingConvAttr(const ParsedAttr &Attrs, CallingConv &CC,
     CC = CC_X86RegCall;
     break;
   case ParsedAttr::AT_MSABI:
-    CC = Context.getTargetInfo().getTriple().isOSWindows() ? CC_C :
-                                                             CC_Win64;
+    CC = Context.getTargetInfo().getTriple().isOSWindowsOrUEFI() ? CC_C
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frobtech wrote:

This really highlights how `getTargetInfo().getCallingConv()` is what we ought to have.  For now it can be defined just this way, but in future it might be controlled by switches within a given target like UEFI.  But right now, it makes code like this and `checkVAStartABI` much clearer.

https://github.com/llvm/llvm-project/pull/124992