arch/sim: Fix usrsock build break on macOS

Signed-off-by: Huang Qi <huangqi3@xiaomi.com>

arch/sim/src/sim/up_usrsock.c

@@ -399,6 +399,7 @@ static const usrsock_handler_t g_usrsock_handler[] =
  * Public Functions
  ****************************************************************************/
 
+__attribute__ ((visibility("default")))
 int usrsock_event_callback(int16_t usockid, uint16_t events)
 {
   return usrsock_send_event(&g_usrsock, usockid, events);