Fix compilation warnings on Android
diff --git a/common/rfb/SDesktop.h b/common/rfb/SDesktop.h
index b4104ea..a41e5be 100644
--- a/common/rfb/SDesktop.h
+++ b/common/rfb/SDesktop.h
@@ -149,7 +149,7 @@
       server = 0;
     }
     virtual void queryConnection(network::Socket* sock,
-                                 const char* userName) {
+                                 __unused_attr const char* userName) {
       server->approveConnection(sock, true, NULL);
     }