Add frontend support for __vectorcall

Wire it through everywhere we have support for fastcall, essentially.

This allows us to parse the MSVC "14" CTP headers, but we will
miscompile them because LLVM doesn't support __vectorcall yet.

Reviewed By: Aaron Ballman

Differential Revision: http://reviews.llvm.org/D5808

llvm-svn: 220573
diff --git a/clang/include/clang-c/Index.h b/clang/include/clang-c/Index.h
index 3892949..6e3bd07 100644
--- a/clang/include/clang-c/Index.h
+++ b/clang/include/clang-c/Index.h
@@ -2853,6 +2853,7 @@
   CXCallingConv_IntelOclBicc = 9,
   CXCallingConv_X86_64Win64 = 10,
   CXCallingConv_X86_64SysV = 11,
+  CXCallingConv_X86VectorCall = 12,
 
   CXCallingConv_Invalid = 100,
   CXCallingConv_Unexposed = 200