lxpanel: use gtk3 by default

pkgs/desktops/lxde/core/lxpanel/default.nix

@@ -7,10 +7,13 @@
 , intltool
 , libxmlxx
 , keybinder
+, keybinder3
 , gtk2
+, gtk3
 , libX11
 , libfm
 , libwnck2
+, libwnck3
 , libXmu
 , libXpm
 , cairo
@@ -21,6 +24,7 @@
 , wirelesstools
 , curl
 , supportAlsa ? false, alsa-lib
+, withGtk3 ? true
 }:
 
 stdenv.mkDerivation rec {
@@ -34,11 +38,11 @@ stdenv.mkDerivation rec {
 
   nativeBuildInputs = [ pkg-config gettext m4 intltool libxmlxx ];
   buildInputs = [
-    keybinder
-    gtk2
+    (if withGtk3 then keybinder3 else keybinder)
+    (if withGtk3 then gtk3 else gtk2)
     libX11
-    libfm
-    libwnck2
+    (libfm.override { inherit withGtk3; })
+    (if withGtk3 then libwnck3 else libwnck2)
     libXmu
     libXpm
     cairo
@@ -58,6 +62,8 @@ stdenv.mkDerivation rec {
       --replace "@PACKAGE_CFLAGS@" "@PACKAGE_CFLAGS@ -I${gdk-pixbuf-xlib.dev}/include/gdk-pixbuf-2.0"
   '';
 
+  configureFlags = lib.optional withGtk3 "--enable-gtk3";
+
   meta = with lib; {
     description = "Lightweight X11 desktop panel for LXDE";
     homepage = "https://lxde.org/";