auto merge of #12175 : sfackler/rust/phase-use-ignored, r=alexcrichton

It could throw an error but I think it's best to not since `#[phase(..)]` syntax in other places would be silently ignored.

Closes #11806

src/test/run-pass/phase-use-ignored.rs

@@ -0,0 +1,19 @@
+// 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.
+
+//xfail-fast
+
+#[feature(phase)];
+
+#[phase(syntax)]
+use std::mem;
+
+fn main() {}
+