proc: Fix race condition when there are many reapers

Use broadcast instead of plain wakeup to make sure no
reaper is left waiting, even though it's thread already
ended, or there're no threads to reap anymore.

JIRA: RTOS-762

proc/threads.c

@@ -481,7 +481,7 @@ static void thread_destroy(thread_t *thread)
 
 		LIST_REMOVE_EX(&process->threads, thread, procnext, procprev);
 		LIST_ADD_EX(&process->ghosts, thread, procnext, procprev);
-		_proc_threadWakeup(&process->reaper);
+		_proc_threadBroadcast(&process->reaper);
 
 		hal_spinlockClear(&threads_common.spinlock, &sc);
 		proc_put(process);
@@ -976,9 +976,10 @@ void proc_reap(void)
 	spinlock_ctx_t sc;
 
 	hal_spinlockSet(&threads_common.spinlock, &sc);
-	while ((ghost = threads_common.ghosts) == NULL)
+	while (threads_common.ghosts == NULL) {
 		_proc_threadWait(&threads_common.reaper, 0, &sc);
-
+	}
+	ghost = threads_common.ghosts;
 	LIST_REMOVE(&threads_common.ghosts, ghost);
 	hal_spinlockClear(&threads_common.spinlock, &sc);