Revert calling convention fix

Author: Prabhuk

clang/lib/Basic/Targets/X86.h

@@ -396,20 +396,9 @@ class LLVM_LIBRARY_VISIBILITY X86TargetInfo : public TargetInfo {
   CallingConvCheckResult checkCallingConvention(CallingConv CC) const override {
     // Most of the non-ARM calling conventions are i386 conventions.
     switch (CC) {
-    case CC_X86ThisCall:
-    case CC_X86FastCall:
-    case CC_X86StdCall:
-    case CC_X86VectorCall:
-    case CC_X86RegCall:
     case CC_C:
-    case CC_PreserveMost:
-    case CC_Swift:
-    case CC_X86Pascal:
-    case CC_IntelOclBicc:
-    case CC_OpenCLKernel:
+    case CC_Win64:
       return CCCR_OK;
-    case CC_SwiftAsync:
-      return CCCR_Error;
     default:
       return CCCR_Warning;
     }