Downgrade ext_enumerator_too_large from ExtWarn to Extension in Microsoft...

Downgrade ext_enumerator_too_large from ExtWarn to Extension in Microsoft mode. Otherwise you can warnings flooding trying to selfhost clang with fms-extensions because of "unsigned int" -> "signed int" enumerator conversion.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@123600 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/Basic/DiagnosticSemaKinds.td

@@ -886,7 +886,7 @@ def err_enum_invalid_underlying : Error<
   "non-integral type %0 is an invalid underlying type">;
 def err_enumerator_too_large : Error<
   "enumerator value is not representable in the underlying type %0">;
-def ext_enumerator_too_large : ExtWarn<
+def ext_enumerator_too_large : Extension<
   "enumerator value is not representable in the underlying type %0">,
   InGroup<Microsoft>;
 def err_enumerator_wrapped : Error<