Add the -Zcrate-attr=foo nightly rustc flag to inject crate attributes

src/test/run-pass/z-crate-attr.rs

@@ -0,0 +1,21 @@
+// Copyright 2018 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.
+
+// This test checks if an unstable feature is enabled with the -Zcrate-attr=feature(foo) flag. If
+// the exact feature used here is causing problems feel free to replace it with another
+// perma-unstable feature.
+
+// compile-flags: -Zcrate-attr=feature(abi_unadjusted)
+
+#![allow(dead_code)]
+
+extern "unadjusted" fn foo() {}
+
+fn main() {}