sigqueue: add signal type judgment logic

To determine whether a signal is real-time signal or standard signal, the POSIX standard https://www.man7.org/linux/man-pages/man7/signal.7.html defines a real-time signal between SIGRTMIN  and SIGRTMAX , which can store multiple copies, otherwise only one can be retained.

Signed-off-by: xinhaiteng <xinhaiteng@xiaomi.com>

sched/signal/sig_dispatch.c

@@ -200,6 +200,13 @@ static FAR sigpendq_t *
 
   DEBUGASSERT(group != NULL);
 
+  /* Determining whether a signal is reliable or unreliable */
+
+  if (SIGRTMIN <= signo && signo <= SIGRTMAX)
+    {
+      return sigpend;
+    }
+
   /* Pending signals can be added from interrupt level. */
 
   flags = enter_critical_section();