Merge ref 'dfe1b8c97bcd' from rust-lang/rust

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

Upstream ref: dfe1b8c97bcde283102f706d5dcdc3649e5e12e3
Filtered ref: 629f327
Upstream diff: rust-lang/rust@caccb4d...dfe1b8c

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

Author: The rustc-josh-sync Cronjob Bot

compiler-builtins/src/lib.rs

@@ -7,7 +7,6 @@
 #![feature(compiler_builtins)]
 #![feature(core_intrinsics)]
 #![feature(linkage)]
-#![feature(asm_cfg)]
 #![feature(naked_functions)]
 #![feature(repr_simd)]
 #![feature(macro_metavar_expr_concat)]