Two's complement does not mean signed overflow became defined. So the check is still wrong. And no, I do not think making it defined would lead to more correct

Two's complement does not mean signed overflow became defined. So the check is still wrong. And no, I do not think making it defined would lead to more correct programs. You then simply have really difficult wrap-around bugs instead of signed overflow which you can be found more easily with UB sanitizer or turn into traps at run-time.