!47 fix mq_notify API

Merge pull request !47 from guweijie/master

porting/liteos_a/user/src/mq/mq_notify.c

+#include <mqueue.h>
+#include <pthread.h>
+#include <errno.h>
+#include <sys/socket.h>
+#include <signal.h>
+#include <unistd.h>
+#include "syscall.h"
+
+int mq_notify(mqd_t mqd, const struct sigevent *sev)
+{
+	if (!sev || sev->sigev_notify != SIGEV_THREAD)
+		return syscall(SYS_mq_notify, mqd, sev);
+
+	errno = ENOTSUP;
+	return -1;
+}