message: incr: cache dwarf objects in work products
  Cache DWARF objects alongside object files in work products when those
  exist so that DWARF object files are available for thorin in packed mode
  in incremental scenarios.
diff: @@ -66,7 +66,11 @@ fn emit_module(
  let work_product = if backend_config.disable_incr_cache {
  None
  } else {
  - rustc_incremental::copy_cgu_workproduct_to_incr_comp_cache_dir(tcx.sess, &name, &tmp_file)
  + rustc_incremental::copy_cgu_workproduct_to_incr_comp_cache_dir(
  + tcx.sess,
  + &name,
  + &[("o", &tmp_file)],
  + )
  };
  ModuleCodegenResult(
  @@ -82,7 +86,10 @@ fn reuse_workproduct_for_cgu(
  ) -> CompiledModule {
  let work_product = cgu.previous_work_product(tcx);
  let obj_out = tcx.output_filenames(()).temp_path(OutputType::Object, Some(cgu.name().as_str()));
  - let source_file = rustc_incremental::in_incr_comp_dir_sess(&tcx.sess, &work_product.saved_file);
  + let source_file = rustc_incremental::in_incr_comp_dir_sess(
  + &tcx.sess,
  + &work_product.saved_files.get("o").expect("no saved object file in work product"),
  + );
  if let Err(err) = rustc_fs_util::link_or_copy(&source_file, &obj_out) {
  tcx.sess.err(&format!(
  "unable to copy {} to {}: {}",
  