Add test for #11677

This code used to cause an ICE

Closes #11677

src/test/run-pass/issue-11677.rs

+// Copyright 2014 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.
+
+#![allow(dead_code)]
+
+// this code used to cause an ICE
+
+trait X<T> {}
+
+struct S<T> {f: Box<X<T>>, g: Box<X<T>>}
+
+struct F;
+impl X<int> for F {}
+
+fn main() {
+  S {f: box F, g: box F};
+}