Add regression test for #18943

Closes #18943.

src/test/run-make/issue-18943/Makefile

@@ -0,0 +1,7 @@
+-include ../tools.mk
+
+# Regression test for ICE #18943 when compiling as lib
+
+all:
+	$(RUSTC) foo.rs --crate-type lib
+	$(call REMOVE_RLIBS,foo) && exit 0 || exit 1

src/test/run-make/issue-18943/foo.rs

@@ -0,0 +1,16 @@
+// Copyright 2015 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.
+
+trait Foo { }
+
+trait Bar { }
+
+impl<'a> Foo for Bar + 'a { }
+