Sema: rename SemaBuiltinVAStart to SemaBuiltinVAStartMicrosoft

This function is used to perform semantic analysis on Microsoft style
`__va_start`.  Rename it to make this more explicit.  `__va_start` is
marked as `ALL_MS_LANGUAGES`, and requires Microsoft compatibility.
Other GNU targets will use `__builtin_va_start` instead.  NFC.

Addresses post-commit review comments from David Majnemer.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@314241 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/Sema/Sema.h

@@ -10264,7 +10264,7 @@ private:
   bool CheckPPCBuiltinFunctionCall(unsigned BuiltinID, CallExpr *TheCall);
 
   bool SemaBuiltinVAStart(unsigned BuiltinID, CallExpr *TheCall);
-  bool SemaBuiltinVAStartARM(CallExpr *Call);
+  bool SemaBuiltinVAStartARMMicrosoft(CallExpr *Call);
   bool SemaBuiltinUnorderedCompare(CallExpr *TheCall);
   bool SemaBuiltinFPClassification(CallExpr *TheCall, unsigned NumArgs);
   bool SemaBuiltinVSX(CallExpr *TheCall);

lib/Sema/SemaChecking.cpp

@@ -833,7 +833,7 @@ Sema::CheckBuiltinFunctionCall(FunctionDecl *FDecl, unsigned BuiltinID,
     switch (Context.getTargetInfo().getTriple().getArch()) {
     case llvm::Triple::arm:
     case llvm::Triple::thumb:
-      if (SemaBuiltinVAStartARM(TheCall))
+      if (SemaBuiltinVAStartARMMicrosoft(TheCall))
         return ExprError();
       break;
     default:
@@ -3924,7 +3924,7 @@ bool Sema::SemaBuiltinVAStart(unsigned BuiltinID, CallExpr *TheCall) {
   return false;
 }
 
-bool Sema::SemaBuiltinVAStartARM(CallExpr *Call) {
+bool Sema::SemaBuiltinVAStartARMMicrosoft(CallExpr *Call) {
   // void __va_start(va_list *ap, const char *named_addr, size_t slot_size,
   //                 const char *named_addr);