gtk2: fix compilation on OS X (by Vincent Snijders, issue #0014533)

git-svn-id: trunk@13674 -

packages/gtk2/src/gtk+/gtk/gtk2.pas

@@ -93,6 +93,7 @@ const
       {$linklib gobject-2.0.0}
       {$linklib gdk_pixbuf-2.0.0}
       {$linklib atk-1.0.0}
+      {$linklib gthread-2.0}
     {$else}
       {$ifdef UseCustomLibs}
       gtklib = '';