Squashed commit of the following:

sched/semaphore:  Add nxsem_post() which is identical to sem_post() except that it never modifies the errno variable.  Changed all references to sem_post in the OS to nxsem_post().

    sched/semaphore:  Add nxsem_destroy() which is identical to sem_destroy() except that it never modifies the errno variable.  Changed all references to sem_destroy() in the OS to nxsem_destroy().

    libc/semaphore and sched/semaphore:  Add nxsem_getprotocol() and nxsem_setprotocola which are identical to sem_getprotocol() and set_setprotocol() except that they never modifies the errno variable.  Changed all references to sem_setprotocol in the OS to nxsem_setprotocol().  sem_getprotocol() was not used in the OS

mm/iob/iob_alloc_qentry.c

@@ -183,7 +183,7 @@ static FAR struct iob_qentry_s *iob_allocwait_qentry(void)
                * we will have to wait again.
                */
 
-              sem_post(&g_qentry_sem);
+              nxsem_post(&g_qentry_sem);
               qentry = iob_tryalloc_qentry();
             }
         }