INT 21 - DOS 2+ - GET RETURN CODE
        AH = 4Dh
Return: AH = termination type
            00h normal (INT 20,INT 21/AH=00h, or INT 21/AH=4Ch)
            01h control-C abort
            02h critical error abort
            03h terminate and stay resident (INT 21/AH=31h or INT 27)
        AL = return code
Notes:  the word in which DOS stores the return code is cleared after being
          read by this function, so the return code can only be retrieved once
        this call should not be used if the child was started with AX=4B04h;
          use AH=8Ah instead
SeeAlso: AH=4Ch,AH=8Ah