avahi: add gtk support

pkgs/development/libraries/avahi/default.nix

@@ -1,5 +1,6 @@
 { fetchurl, stdenv, pkgconfig, libdaemon, dbus, perlPackages
 , expat, gettext, intltool, glib, libiconv
+, gtk3Support ? false, gtk3 ? null
 , qt4 ? null
 , qt4Support ? false
 , withLibdnssdCompat ? false }:
@@ -19,13 +20,15 @@ stdenv.mkDerivation rec {
 
   buildInputs = [ libdaemon dbus glib expat libiconv ]
     ++ (with perlPackages; [ perl XMLParser ])
+    ++ (stdenv.lib.optional gtk3Support gtk3)
     ++ (stdenv.lib.optional qt4Support qt4);
 
   nativeBuildInputs = [ pkgconfig gettext intltool glib ];
 
   configureFlags =
     [ "--disable-qt3" "--disable-gdbm" "--disable-mono"
-      "--disable-gtk" "--disable-gtk3"
+      "--disable-gtk"
+      (stdenv.lib.enableFeature gtk3Support "gtk3")
       "--${if qt4Support then "enable" else "disable"}-qt4"
       "--disable-python" "--localstatedir=/var" "--with-distro=none"
       # A systemd unit is provided by the avahi-daemon NixOS module