Fix a few issues with latest GTK scaling changes

* src/xfns.c (Fx_display_monitor_attributes_list): Call
gdk_screen_get_monitor_scale_factor only for GTK versions
3.10..3.21.
* src/xterm.c (x_set_offset): Call xg_get_scale for GTK only.

src/xfns.c

@@ -4940,7 +4940,7 @@ Internal use only, use `display-monitor-attributes-list' instead.  */)
       gint width_mm = -1, height_mm = -1;
       GdkRectangle rec, work;
       struct MonitorInfo *mi = &monitors[i];
-      int scale;
+      int scale = 1;
 
 #if GTK_CHECK_VERSION (3, 22, 0)
       GdkMonitor *monitor = gdk_display_get_monitor (gdpy, i);
@@ -4989,7 +4989,7 @@ Internal use only, use `display-monitor-attributes-list' instead.  */)
       /* GTK returns scaled sizes for the workareas.  */
 #if GTK_CHECK_VERSION (3, 22, 0)
       scale = gdk_monitor_get_scale_factor (monitor);
-#else
+#elif GTK_CHECK_VERSION (3, 10, 0)
       scale = gdk_screen_get_monitor_scale_factor (gscreen, i);
 #endif
       rec.width *= scale;

src/xterm.c

@@ -10310,7 +10310,9 @@ void
 x_set_offset (struct frame *f, register int xoff, register int yoff, int change_gravity)
 {
   int modified_top, modified_left;
+#ifdef USE_GTK
   int scale = xg_get_scale (f);
+#endif
 
   if (change_gravity > 0)
     {