Fix a thinko and a test.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@70637 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/SemaCXX/offsetof.cpp b/test/SemaCXX/offsetof.cpp
index c8a3d3d..f0290e8 100644
--- a/test/SemaCXX/offsetof.cpp
+++ b/test/SemaCXX/offsetof.cpp
@@ -1,4 +1,4 @@
-// RUN: clang-cc -fsyntax-only -verify %s
+// RUN: clang-cc -fsyntax-only -verify %s -Winvalid-offsetof
 
 struct NonPOD {
   virtual void f();