[CodeGen] Handle __func__ inside __finally

When we enter a __finally block, the CGF's CurCodeDecl will be null
(because CodeGenFunction::StartFunction is given an empty GlobalDecl for
a __finally block), and so the dyn_cast here will result in an assertion
failure. Change it to dyn_cast_or_null to handle this case.

Differential Revision: https://reviews.llvm.org/D45523

llvm-svn: 329836
diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index ba34208..55b67db 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -2611,7 +2611,7 @@
   StringRef NameItems[] = {
       PredefinedExpr::getIdentTypeName(E->getIdentType()), FnName};
   std::string GVName = llvm::join(NameItems, NameItems + 2, ".");
-  if (auto *BD = dyn_cast<BlockDecl>(CurCodeDecl)) {
+  if (auto *BD = dyn_cast_or_null<BlockDecl>(CurCodeDecl)) {
     std::string Name = SL->getString();
     if (!Name.empty()) {
       unsigned Discriminator =