Index: lib/Basic/Targets.cpp
===================================================================
--- lib/Basic/Targets.cpp
+++ lib/Basic/Targets.cpp
@@ -4959,6 +4959,19 @@
   BuiltinVaListKind getBuiltinVaListKind() const override {
     return TargetInfo::CharPtrBuiltinVaList;
   }
+  CallingConvCheckResult checkCallingConvention(CallingConv CC) const override {
+    switch (CC) {
+    case CC_X86StdCall:
+    case CC_X86ThisCall:
+    case CC_X86FastCall:
+    case CC_X86VectorCall:
+      return CCCR_Ignore;
+    case CC_C:
+      return CCCR_OK;
+    default:
+      return CCCR_Warning;
+    }
+  }
 };
 
 // Windows ARM + Itanium C++ ABI Target
Index: test/Parser/arm-windows-calling-convention-handling.c
===================================================================
--- test/Parser/arm-windows-calling-convention-handling.c
+++ test/Parser/arm-windows-calling-convention-handling.c
@@ -1,10 +1,9 @@
 // RUN: %clang_cc1 -triple thumbv7-windows -fms-compatibility -fsyntax-only -verify %s
 
-int __cdecl cdecl(int a, int b, int c, int d) { // expected-warning {{calling convention '__cdecl' ignored for this target}}
+int __cdecl cdecl(int a, int b, int c, int d) { // expected-no-diagnostics
   return a + b + c + d;
 }
 
-float __stdcall stdcall(float a, float b, float c, float d) { // expected-warning {{calling convention '__stdcall' ignored for this target}}
+float __stdcall stdcall(float a, float b, float c, float d) { // expected-no-diagnostics
   return a + b + c + d;
 }
-
Index: test/Parser/x64-windows-calling-convention-handling.c
===================================================================
--- /dev/null
+++ test/Parser/x64-windows-calling-convention-handling.c
@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 -triple x86_64-windows -fms-compatibility -fsyntax-only -verify %s
+
+int __cdecl cdecl(int a, int b, int c, int d) { // expected-no-diagnostics
+  return a + b + c + d;
+}
+
+float __stdcall stdcall(float a, float b, float c, float d) { // expected-no-diagnostics
+  return a + b + c + d;
+}