use of predefined identifiers like __func__ at global scope warn in sema,
but crashed codegen.  Fix this to report the name of the llvm function.
This fixes rdar://6808051


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@69658 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/CGExpr.cpp b/lib/CodeGen/CGExpr.cpp
index 906a1e2..3ca625c 100644
--- a/lib/CodeGen/CGExpr.cpp
+++ b/lib/CodeGen/CGExpr.cpp
@@ -753,7 +753,7 @@
   }
 
   std::string FunctionName;
-  if(const FunctionDecl *FD = dyn_cast<FunctionDecl>(CurFuncDecl)) {
+  if (const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(CurFuncDecl)) {
     FunctionName = CGM.getMangledName(FD);
   } else {
     // Just get the mangled name; skipping the asm prefix if it