xfce4-panel: fix tzdata path

pkgs/desktops/xfce/core/xfce4-panel.nix

···
 { stdenv, fetchurl, pkgconfig, intltool, gtk, libxfce4util, libxfce4ui
 , libxfce4ui_gtk3, libwnck, exo, garcon, xfconf, libstartup_notification
-, makeWrapper, xfce4-mixer, hicolor-icon-theme
+, makeWrapper, xfce4-mixer, hicolor-icon-theme, tzdata
 , withGtk3 ? false, gtk3, gettext, glib-networking
 }:
 let
···
     for f in $(find . -name \*.sh); do
       substituteInPlace $f --replace gettext ${gettext}/bin/gettext
     done
+    substituteInPlace plugins/clock/clock.c \
+       --replace "/usr/share/zoneinfo" "${tzdata}/share/zoneinfo" \
+       --replace "if (!g_file_test (filename, G_FILE_TEST_IS_SYMLINK))" ""
   '';
 
   outputs = [ "out" "dev" "devdoc" ];

pkgs/desktops/xfce4-13/xfce4-panel/default.nix

···
-{ mkXfceDerivation, exo, garcon, gtk2, gtk3, libxfce4ui, libxfce4util, libwnck3, xfconf }:
+{ mkXfceDerivation, tzdata, exo, garcon, gtk2, gtk3, libxfce4ui, libxfce4util, libwnck3, xfconf }:
 
 mkXfceDerivation rec {
   category = "xfce";
···
   sha256 = "194pihmg7af4x81nia2fy3h7rls306a7c0bqny9ycqikvi6nmdmn";
 
   buildInputs = [ exo garcon gtk2 gtk3 libxfce4ui libxfce4util libwnck3 xfconf ];
+
+  postPatch = ''
+    substituteInPlace plugins/clock/clock.c \
+       --replace "/usr/share/zoneinfo" "${tzdata}/share/zoneinfo" \
+       --replace "if (!g_file_test (filename, G_FILE_TEST_IS_SYMLINK))" ""
+  '';
 
   meta =  {
     description = "Xfce's panel";