`mrb_class_real()` did not work for `BasicObject`; fix #4037
mrb_notimplement_m(mrb_state *mrb, mrb_value self)
{
  mrb_notimplement(mrb);
  /* not reached */
  return mrb_nil_value();
}

mrb_notimplement_m(mrb_state *mrb, mrb_value self)
{
  mrb_notimplement(mrb);
  /* not reached */
  return mrb_nil_value();
}
