[AArch64] Add support for __builtin_ms_va_list on aarch64

Move builtins from the x86 specific scope into the global
scope. Their use is still limited to x86_64 and aarch64 though.

This allows wine on aarch64 to properly handle variadic functions.

Differential Revision: https://reviews.llvm.org/D34475

llvm-svn: 308218
diff --git a/clang/lib/AST/MicrosoftMangle.cpp b/clang/lib/AST/MicrosoftMangle.cpp
index 3a899bd..24b16f8 100644
--- a/clang/lib/AST/MicrosoftMangle.cpp
+++ b/clang/lib/AST/MicrosoftMangle.cpp
@@ -2122,7 +2122,7 @@
   switch (CC) {
     default:
       llvm_unreachable("Unsupported CC for mangling");
-    case CC_X86_64Win64:
+    case CC_Win64:
     case CC_X86_64SysV:
     case CC_C: Out << 'A'; break;
     case CC_X86Pascal: Out << 'C'; break;