Put ifdef around tray.h functions

Only define in case we built with GTK support.

src/ui/tray.h

@@ -35,22 +35,15 @@
 #ifndef UI_TRAY_H
 #define UI_TRAY_H
 
+#ifdef HAVE_GTK
 void tray_init(void);
 void tray_update(void);
 void tray_shutdown(void);
 
-/*
- * Create tray icon
- *
- * This will initialize the timer that will be called in order to change the icons
- * and will search the icons in the defaults paths
- */
 void tray_enable(void);
-/*
- * Destroy tray icon
- */
 void tray_disable(void);
 
 void tray_set_timer(int interval);
+#endif
 
 #endif