message: remove no longer needed (and sometimes broken) 'extern crate'
diff: #![feature(rustc_private)]
  -extern crate getopts;
  extern crate miri;
  extern crate rustc;
  -extern crate rustc_codegen_utils;
  extern crate rustc_driver;
  -extern crate rustc_errors;
  extern crate rustc_hir;
  extern crate rustc_interface;
  -extern crate rustc_metadata;
  extern crate rustc_span;
  use std::io;
  