SL-16330 mac build fix

indra/newview/llviewercontrol.cpp

@@ -243,7 +243,9 @@ static bool handleAnisotropicChanged(const LLSD& newvalue)
 
 static bool handleVSyncChanged(const LLSD& newvalue)
 {
+#if LL_WINDOWS
     gViewerWindow->getWindow()->toggleVSync(newvalue.asBoolean());
+#endif
     return true;
 }