Fix build on PGTK

* src/gtkutil.c (xg_mark_data):
* src/gtkutil.h (xg_filter_key): Ifdef out definitions on PGTK.

src/gtkutil.c

@@ -2956,6 +2956,7 @@ xg_mark_data (void)
         }
     }
 
+#ifndef HAVE_PGTK
   if (xg_pending_quit_event.kind != NO_EVENT)
     {
       eassert (xg_pending_quit_event.kind == ASCII_KEYSTROKE_EVENT);
@@ -2963,6 +2964,7 @@ xg_mark_data (void)
       mark_object (xg_pending_quit_event.frame_or_window);
       mark_object (xg_pending_quit_event.arg);
     }
+#endif
 }
 
 /* Callback called when a menu item is destroyed.  Used to free data.

src/gtkutil.h

@@ -217,7 +217,9 @@ extern void xg_print_frames_dialog (Lisp_Object);
 extern bool xg_is_menu_window (Display *dpy, Window);
 #endif
 
+#ifndef HAVE_PGTK
 extern bool xg_filter_key (struct frame *frame, XEvent *xkey);
+#endif
 
 /* Mark all callback data that are Lisp_object:s during GC.  */
 extern void xg_mark_data (void);