conformtest: Allow time.h inclusion from semaphore.h for XOPEN2K.

POSIX.1:2001 added sem_timedwait, but said nothing about defining
struct timespec in semaphore.h.  The 2008 edition added a
corresponding permission to include <time.h> from <semaphore.h>.
Since this is the normal POSIX approach in such cases, it seems
appropriate to consider this a bug fix, and so this patch makes the
conform/ tests allow that inclusion for POSIX.1:2001 as well.

Tested for x86_64.

	* conform/data/semaphore.h-data [XOPEN2K] (time.h): Allow header
	inclusion.
	* conform/Makefile (test-xfail-XOPEN2K/semaphore.h/conform):
	Remove.