MINOR: wdt: do not depend on USE_THREAD

There is no reason for restricting the use of the watchdog to threads
anymore, as it works perfectly without threads as well.
diff --git a/src/wdt.c b/src/wdt.c
index 4adc33d..528685a 100644
--- a/src/wdt.c
+++ b/src/wdt.c
@@ -25,7 +25,7 @@
  * It relies on timer_create() and timer_settime() which are only available in
  * this case.
  */
-#if defined(USE_THREAD) && defined(USE_RT) && (_POSIX_TIMERS > 0) && defined(_POSIX_THREAD_CPUTIME)
+#if defined(USE_RT) && (_POSIX_TIMERS > 0) && defined(_POSIX_THREAD_CPUTIME)
 
 /* We'll deliver SIGALRM when we've run out of CPU as it's not intercepted by
  * gdb by default.
@@ -117,9 +117,11 @@
 	 * with the other thread interrupted exactly where it was running and
 	 * the current one not involved in this.
 	 */
+#ifdef USE_THREAD
 	if (thr != tid)
 		pthread_kill(ha_thread_info[thr].pthread, sig);
 	else
+#endif
 		ha_panic();
 	return;