use CodeGenModule::EmitNullConstant in a couple of places.

llvm-svn: 77915
diff --git a/clang/lib/CodeGen/CGExprConstant.cpp b/clang/lib/CodeGen/CGExprConstant.cpp
index dbb1bdc..3a1eac9 100644
--- a/clang/lib/CodeGen/CGExprConstant.cpp
+++ b/clang/lib/CodeGen/CGExprConstant.cpp
@@ -772,5 +772,5 @@
 llvm::Constant *CodeGenModule::EmitNullConstant(QualType T) {
   // Always return an LLVM null constant for now; this will change when we
   // get support for IRGen of member pointers.
-  return llvm::Constant::getNullValue(getTypes().ConvertType(T));
+  return llvm::Constant::getNullValue(getTypes().ConvertTypeForMem(T));
 }