message: Split flags whitespace
  This is probably the wrong way to do this...
diff: @@ -417,9 +417,7 @@ fn rustc_command<I, S>(&self, args: I) -> Command
  rustc_clif.push(get_wrapper_file_name("rustc-clif", "bin", &self.host_triple));
  let mut cmd = Command::new(rustc_clif);
  - if !self.rust_flags.is_empty() {
  - cmd.arg(&self.rust_flags);
  - }
  + cmd.args(self.rust_flags.split_whitespace());
  cmd.arg("-L");
  cmd.arg(format!("crate={}", self.out_dir.display()));
  cmd.arg("--out-dir");
  