posix-timers: Make them configurable

Some embedded systems have no use for them.  This removes about
25KB from the kernel binary size when configured out.

Corresponding syscalls are routed to a stub logging the attempt to
use those syscalls which should be enough of a clue if they were
disabled without proper consideration. They are: timer_create,
timer_gettime: timer_getoverrun, timer_settime, timer_delete,
clock_adjtime, setitimer, getitimer, alarm.

The clock_settime, clock_gettime, clock_getres and clock_nanosleep
syscalls are replaced by simple wrappers compatible with CLOCK_REALTIME,
CLOCK_MONOTONIC and CLOCK_BOOTTIME only which should cover the vast
majority of use cases with very little code.

Signed-off-by: Nicolas Pitre <nico@linaro.org>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: John Stultz <john.stultz@linaro.org>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Cc: Paul Bolle <pebolle@tiscali.nl>
Cc: linux-kbuild@vger.kernel.org
Cc: netdev@vger.kernel.org
Cc: Michal Marek <mmarek@suse.com>
Cc: Edward Cree <ecree@solarflare.com>
Link: http://lkml.kernel.org/r/1478841010-28605-7-git-send-email-nicolas.pitre@linaro.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

security/selinux/hooks.c

@@ -2525,7 +2525,8 @@ static void selinux_bprm_committing_creds(struct linux_binprm *bprm)
 			rlim->rlim_cur = min(rlim->rlim_max, initrlim->rlim_cur);
 		}
 		task_unlock(current);
-		update_rlimit_cpu(current, rlimit(RLIMIT_CPU));
+		if (IS_ENABLED(CONFIG_POSIX_TIMERS))
+			update_rlimit_cpu(current, rlimit(RLIMIT_CPU));
 	}
 }
 
@@ -2555,9 +2556,11 @@ static void selinux_bprm_committed_creds(struct linux_binprm *bprm)
 	 */
 	rc = avc_has_perm(osid, sid, SECCLASS_PROCESS, PROCESS__SIGINH, NULL);
 	if (rc) {
-		memset(&itimer, 0, sizeof itimer);
-		for (i = 0; i < 3; i++)
-			do_setitimer(i, &itimer, NULL);
+		if (IS_ENABLED(CONFIG_POSIX_TIMERS)) {
+			memset(&itimer, 0, sizeof itimer);
+			for (i = 0; i < 3; i++)
+				do_setitimer(i, &itimer, NULL);
+		}
 		spin_lock_irq(&current->sighand->siglock);
 		if (!fatal_signal_pending(current)) {
 			flush_sigqueue(&current->pending);