Merge ref '4c4205163abc' from rust-lang/rust

Pull recent changes from https://github.com/rust-lang/rust via Josh.

Upstream ref: rust-lang/rust@4c42051
Filtered ref: ec550d4
Upstream diff: rust-lang/rust@80ad557...4c42051

This merge was created using https://github.com/rust-lang/josh-sync.

Author: lnicola