XQuartz: use a condition variable to signal when darwinEvents is ready rather than polling

(cherry picked from commit ff1c443cadf11d12a7d939e51194f6105153870e)

hw/xquartz/mach-startup/bundle-main.c

@@ -412,11 +412,6 @@ int main(int argc, char **argv, char **envp) {
 }
 #else
 void *add_launchd_display_thread(void *data) {
-    /* TODO: Really fix this race... we want xinitrc to finish before connections
-     *       are accepted on the launchd socket.
-     */
-    sleep(2);
-    
     /* Start listening on the launchd fd */
     int launchd_fd = launchd_display_fd();
     if(launchd_fd != -1) {