code: def STREX(cpu, status, *args):
          
          # TODO: implement conditional return with appropriate status --GR, 2017-06-06
          status.write(0)
          return cpu._STR(cpu.address_bit_size, *args)
docs: STREX performs a conditional store to memory.
          :param Armv7Operand status: the destination register for the returned status; register