Treat __extension__ like ParenExpr.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@116569 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/Parser/expressions.c b/test/Parser/expressions.c
index ffc5c83..6015e91 100644
--- a/test/Parser/expressions.c
+++ b/test/Parser/expressions.c
@@ -39,7 +39,8 @@
 
 // PR3418
 int test_leading_extension() {
-  __extension__ (*(char*)0) = 1;
+  __extension__ (*(char*)0) = 1; // expected-warning {{indirection of non-volatile null pointer}} \
+                                 // expected-note {{consider using __builtin_trap}}
   return 0;
 }