Add Microsoft Mangling for OpenCL Half Type

[vbridgers]

Summary

Half-type mangling is accomplished following the method introduced by Erich Keane for mangling _Float16. Updated the half.cl LIT test to cover this particular case.

[rnk]

lgtm

cfe/trunk/lib/AST/MicrosoftMangle.cpp

case BuiltinType::NullPtr:
     Out << "$$T";
     break;
 
   case BuiltinType::Char8:
   case BuiltinType::Float16:
     mangleArtificalTagType(TTK_Struct, "_Float16", {"__clang"});
     break;
 
-  case BuiltinType::Float128:
-  case BuiltinType::Half: {
+  case BuiltinType::Half:
+    mangleArtificalTagType(TTK_Struct, "_Half", {"__clang"});
+    break;
+
+  case BuiltinType::Float128: {
     DiagnosticsEngine &Diags = Context.getDiags();
     unsigned DiagID = Diags.getCustomDiagID(
         DiagnosticsEngine::Error, "cannot mangle this built-in %0 type yet");
     Diags.Report(Range.getBegin(), DiagID)
         << T->getName(Context.getASTContext().getPrintingPolicy()) << Range;
     break;
   }
   }

cfe/trunk/test/CodeGenOpenCL/half.cl

 // RUN: %clang_cc1 %s -emit-llvm -o - -triple spir-unknown-unknown | FileCheck %s
+// RUN: %clang_cc1 %s -emit-llvm -o - -triple x86_64-pc-win32 | FileCheck %s
 
 #pragma OPENCL EXTENSION cl_khr_fp16 : enable
 
 
 half test()
 {
    half x = 0.1f;
    x+=2.0f;