Merge ref '55e86c996809' from rust-lang/rust

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

Upstream ref: rust-lang/rust@55e86c996809902e8bbad512cfb4d2c18be446d9
Filtered ref: rust-lang/miri@b7da5a7e0b02030b279bb199bf5006dbdec57f72
Upstream diff: https://github.com/rust-lang/rust/compare/12ab1cf1fd3dc925a846b0eb8a4b39393140fdd3...55e86c996809902e8bbad512cfb4d2c18be446d9

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