message: Print hex dump of alloc on reading undef bytes
diff: @@ -114,6 +114,9 @@ pub fn report_error<'tcx, 'mir>(
  };
  e.print_backtrace();
  + if let UndefinedBehavior(UndefinedBehaviorInfo::InvalidUndefBytes(Some(ptr))) = e.kind {
  + ecx.memory.dump_alloc(ptr.alloc_id);
  + }
  let msg = e.to_string();
  report_msg(ecx, &format!("{}: {}", title, msg), msg, helps, true)
  }
  