pop-gtk-theme: fix cross-compilation (#423455)

pkgs/by-name/po/pop-gtk-theme/package.nix

@@ -12,6 +12,7 @@
   gdk-pixbuf,
   librsvg,
   python3,
+  buildPackages,
 }:
 
 stdenv.mkDerivation {
@@ -50,9 +51,9 @@ stdenv.mkDerivation {
     for file in $(find -name render-\*.sh); do
       substituteInPlace "$file" \
         --replace 'INKSCAPE="/usr/bin/inkscape"' \
-                  'INKSCAPE="${inkscape}/bin/inkscape"' \
+                  'INKSCAPE="${buildPackages.inkscape}/bin/inkscape"' \
         --replace 'OPTIPNG="/usr/bin/optipng"' \
-                  'OPTIPNG="${optipng}/bin/optipng"'
+                  'OPTIPNG="${buildPackages.optipng}/bin/optipng"'
     done
   '';