Made the "expected string literal" diagnostic more expressive

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@168267 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/Sema/static-assert.c b/test/Sema/static-assert.c
index 13d7070..9309987 100644
--- a/test/Sema/static-assert.c
+++ b/test/Sema/static-assert.c
@@ -9,3 +9,5 @@
   _Static_assert(1, "1 is nonzero");
   _Static_assert(0, "0 is nonzero"); // expected-error {{static_assert failed "0 is nonzero"}}
 }
+
+_Static_assert(1, invalid); // expected-error {{expected string literal for diagnostic message in static_assert}}