Fix compilation of server.cc on hpux.

Select and FD_ISSET are declared in sys/time.h on most versions
of hpux.  As a result, HAVE_PSELECT and HAVE_SELECT can be 0.

2023-01-08  John David Anglin  <danglin@gcc.gnu.org>

c++tools/ChangeLog:

	PR other/107616
	* server.cc (server): Don't call FD_ISSET when HAVE_PSELECT
	and HAVE_SELECT are zero.