fix: clear error compilation of signal in qemu-a9 smp mode

Author: kurisaW

include/rtthread.h

@@ -253,6 +253,7 @@ void rt_scheduler_ipi_handler(int vector, void *param);
 #ifdef RT_USING_SIGNALS
 void rt_signal_mask(int signo);
 void rt_signal_unmask(int signo);
+void *rt_signal_check(void* context);
 rt_sighandler_t rt_signal_install(int signo, rt_sighandler_t handler);
 int rt_signal_wait(const rt_sigset_t *set, rt_siginfo_t *si, rt_int32_t timeout);
 int rt_system_signal_init(void);