Suppress unused parameter warning in wxX11

It seems better to keep it for consistency, as all the other functions
take both Drawable and GC, but it isn't being used in this particular
function.

src/x11/pango_x.cpp

@@ -57,7 +57,7 @@ x11_pango_get_item_properties( PangoItem      *item,
 
 void
 x11_draw_glyphs( Drawable            drawable,
-                 GC                  gc,
+                 GC                  WXUNUSED(gc),
                  PangoFont          *font,
                  int                 x,
                  int                 y,