Remove #[macro_use] extern crate bitflags

Author: taiki-e

src/librustc_mir/lib.rs

@@ -33,8 +33,6 @@ Rust MIR: a lowered representation of Rust. Also: an experiment!
 #![deny(rust_2018_idioms)]
 #![allow(explicit_outlives_requirements)]
 
-#[macro_use]
-extern crate bitflags;
 #[macro_use] extern crate log;
 #[macro_use]
 extern crate rustc;

src/librustc_mir/transform/qualify_consts.rs

@@ -30,7 +30,7 @@ use std::usize;
 use crate::transform::{MirPass, MirSource};
 use super::promote_consts::{self, Candidate, TempState};
 
-bitflags! {
+bitflags::bitflags! {
     // Borrows of temporaries can be promoted only if
     // they have none of these qualifications, with
     // the exception of `STATIC_REF` (in statics only).