message: don't have both MIRI_SYSROOT and --sysroot
diff: @@ -458,6 +458,7 @@ fn inside_cargo_rustc() {
  } else {
  Command::new("rustc")
  };
  + command.env_remove("MIRI_SYSROOT"); // we already set the --sysroot flag
  command.args(&args);
  if has_arg_flag("-v") {
  eprintln!("+ {:?}", command);
  