Provide half floating point support as a storage only type.
Lack of half FP was a regression compared to llvm-gcc.

llvm-svn: 142016
diff --git a/clang/lib/AST/MicrosoftMangle.cpp b/clang/lib/AST/MicrosoftMangle.cpp
index e327d8b..1515db4 100644
--- a/clang/lib/AST/MicrosoftMangle.cpp
+++ b/clang/lib/AST/MicrosoftMangle.cpp
@@ -713,6 +713,7 @@
 
   case BuiltinType::Char16:
   case BuiltinType::Char32:
+  case BuiltinType::Half:
   case BuiltinType::NullPtr:
     llvm_unreachable("Don't know how to mangle this type");
   }