Add regression test

src/test/compile-fail-fulldeps/expanded-macro-use.rs

@@ -0,0 +1,19 @@
+// 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_private)]
+macro_rules! m {
+    () => { #[macro_use] extern crate syntax; }
+}
+m!();
+
+fn main() {
+    help!(); //~ ERROR unexpected end of macro invocation
+}