sched/signal: Fix build warning when signals are disabled

Fix a build warning that occurs when signal support is disabled.

Signed-off-by: Chengdong Wang <wangchengdong@lixiang.com>

Author: wangchdo

fs/vfs/fs_epoll.c

@@ -724,7 +724,9 @@ int epoll_pwait(int epfd, FAR struct epoll_event *evs,
 {
   FAR struct file *filep;
   FAR epoll_head_t *eph;
+#ifndef CONFIG_DISABLE_SIGNALS
   sigset_t oldsigmask;
+#endif
   int ret;
 
   eph = epoll_head_from_fd(epfd, &filep);

sched/pthread/pthread_exit.c

@@ -65,7 +65,9 @@
 void nx_pthread_exit(FAR void *exit_value)
 {
   FAR struct tcb_s *tcb = this_task();
+#ifndef CONFIG_DISABLE_SIGNALS
   sigset_t set;
+#endif
   int status;
 
   sinfo("exit_value=%p\n", exit_value);

sched/task/task_setup.c

@@ -403,7 +403,6 @@ static int nxthread_setup_scheduler(FAR struct tcb_s *tcb, int priority,
                                     start_t start, CODE void *entry,
                                     uint8_t ttype)
 {
-  FAR struct tcb_s *rtcb = this_task();
   irqstate_t flags;
   int ret;
 
@@ -462,7 +461,7 @@ static int nxthread_setup_scheduler(FAR struct tcb_s *tcb, int priority,
        * inherit the signal mask of the parent thread.
        */
 
-      tcb->sigprocmask = rtcb->sigprocmask;
+      tcb->sigprocmask = this_task()->sigprocmask;
 #endif
 
       /* Initialize the task state.  It does not get a valid state