gnome.gnome-session: Make support for GNOME Shell optional

Signed-off-by: Federico Damián Schonborn <fdschonborn@gmail.com>

pkgs/desktops/gnome/core/gnome-session/default.nix

@@ -25,6 +25,7 @@
 , libepoxy
 , bash
 , gnome-session-ctl
+, gnomeShellSupport ? true
 }:
 
 stdenv.mkDerivation rec {
@@ -113,7 +114,7 @@ stdenv.mkDerivation rec {
     wrapProgram "$out/libexec/gnome-session-binary" \
       --prefix GI_TYPELIB_PATH : "$GI_TYPELIB_PATH" \
       --suffix XDG_DATA_DIRS : "$out/share:$GSETTINGS_SCHEMAS_PATH" \
-      --suffix XDG_DATA_DIRS : "${gnome.gnome-shell}/share"\
+      ${lib.optionalString gnomeShellSupport "--suffix XDG_DATA_DIRS : \"${gnome.gnome-shell}/share\""} \
       --suffix XDG_CONFIG_DIRS : "${gnome.gnome-settings-daemon}/etc/xdg"
   '';