message: Add profile code around metadata object generation
  cc
diff: @@ -215,6 +215,8 @@ fn run_aot(
  rustc_incremental::finalize_session_directory(tcx.sess, tcx.crate_hash(LOCAL_CRATE));
  let metadata_module = if need_metadata_module {
  + tcx.sess.profiler(|p| p.start_activity("codegen crate metadata"));
  + let (metadata_cgu_name, tmp_file) = rustc::util::common::time(tcx.sess, "write compressed metadata", || {
  use rustc::mir::mono::CodegenUnitNameBuilder;
  let cgu_name_builder = &mut CodegenUnitNameBuilder::new(tcx);
  @@ -236,6 +238,10 @@ fn run_aot(
  let obj = metadata_artifact.emit().unwrap();
  std::fs::write(&tmp_file, obj).unwrap();
  + (metadata_cgu_name, tmp_file)
  + });
  + tcx.sess.profiler(|p| p.end_activity("codegen crate metadata"));
  +
  Some(CompiledModule {
  name: metadata_cgu_name,
  kind: ModuleKind::Metadata,
  