Add regression test

Author: jseyfried

src/test/compile-fail/expanded-cfg.rs

@@ -0,0 +1,26 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![feature(rustc_attrs)]
+
+macro_rules! mac {
+    {} => {
+        #[cfg(attr)]
+        mod m {
+            #[lang_item]
+            fn f() {}
+        }
+    }
+}
+
+mac! {}
+
+#[rustc_error]
+fn main() {} //~ ERROR compilation successful