bug#9839: compile with gdb running

[Glenn Morris]

A comment about the change in question is given in

http://debbugs.gnu.org/cgi/bugreport.cgi?bug=4437#30

    This allows the I/O buffer to work when the inferior is restarted
    but means that status_notify isn't called from
    wait_reading_process_output because this call is conditioned on
    select which returns a positive value (presumably because the pty's
    file descriptor hasn't been cleared). Reverting it means processes
    aren't left lying around but that leaves the original problem.