Include a simple test case for the previous commit...

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@43158 91177308-0d34-0410-b5e6-96231b3b80d8

test/Sema/missing-string-interface.m

@@ -0,0 +1,7 @@
+// RUN: clang %s -verify -fsyntax-only
+
+@class NSString;
+
+// GCC considers this an error, so clang will...
+NSString *s = @"123"; // expected-error: {{cannot find interface declaration for 'NSConstantString'}}
+