Avoid hangs in accept-process-output.

Avoid hangs in accept-process-output.

* lisp.h, process.c (wait_reading_process_input):
Return int, not bool.  All uses changed.
* process.c (SELECT_CANT_DO_WRITE_MASK):
Remove macro, replacing with ...
(SELECT_CAN_DO_WRITE_MASK): ... new constant, with inverted sense.
All uses changed.
(status_notify): New arg WAIT_PROC.  Return int, not void.
All uses changed.

Fixes: debbugs:17647