message: Implement atomic_singlethreadfence_*
diff: @@ -889,6 +889,7 @@ fn codegen_intrinsic_call<'a, 'tcx: 'a>(
  ret.write_cvalue(fx, needs_drop);
  }
  _ if intrinsic.starts_with("atomic_fence") => {}
  + _ if intrinsic.starts_with("atomic_singlethreadfence") => {}
  _ if intrinsic.starts_with("atomic_load") => {
  assert_eq!(args.len(), 1);
  let inner_layout =
  