wlogout: disable gtk-layer-shell when cross-compiling

Because gtk-layer-shell doesn't cross-compile properly

pkgs/tools/wayland/wlogout/default.nix

@@ -10,6 +10,11 @@
 , wayland
 , wayland-protocols
 , gtk-layer-shell
+# gtk-layer-shell fails to cross-compile due to a hard dependency
+# on gobject-introspection.
+# Disable it when cross-compiling since it's an optional dependency.
+# This disables transparency support.
+, withGtkLayerShell ? (stdenv.buildPlatform == stdenv.hostPlatform)
 }:
 
 stdenv.mkDerivation rec {
@@ -30,6 +35,7 @@ stdenv.mkDerivation rec {
     libxkbcommon
     wayland
     wayland-protocols
+  ] ++ lib.optionals withGtkLayerShell [
     gtk-layer-shell
   ];