Don't crash when our FunctionDecl has a non-identifier name

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@61970 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/Driver/RewriteObjC.cpp b/Driver/RewriteObjC.cpp
index b20bbb3..62aed79 100644
--- a/Driver/RewriteObjC.cpp
+++ b/Driver/RewriteObjC.cpp
@@ -1942,7 +1942,8 @@
 
 void RewriteObjC::RewriteFunctionDecl(FunctionDecl *FD) {
   // declared in <objc/objc.h>
-  if (strcmp(FD->getNameAsCString(), "sel_registerName") == 0) {
+  if (FD->getIdentifier() &&
+      strcmp(FD->getNameAsCString(), "sel_registerName") == 0) {
     SelGetUidFunctionDecl = FD;
     return;
   }