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

drivers/dev_null.c

@@ -116,7 +116,7 @@ static int devnull_poll(FAR struct file *filep, FAR struct pollfd *fds,
       fds->revents |= (fds->events & (POLLIN | POLLOUT));
       if (fds->revents != 0)
         {
-          sem_post(fds->sem);
+          nxsem_post(fds->sem);
         }
     }