message: Group some commonly passed together values into a struct
diff: @@ -75,7 +75,7 @@ impl rustc_driver::Callbacks for MiriCompilerCalls {
  let mut config = self.miri_config.clone();
  // Add filename to `miri` arguments.
  - config.args.insert(0, compiler.input().filestem().to_string());
  + config.args.insert(0, compiler.io().input.filestem().to_string());
  // Adjust working directory for interpretation.
  if let Some(cwd) = env::var_os("MIRI_CWD") {
  