GTK stock images aren't available using other vcl plugins

Change-Id: I5ab23733d8d9c71fcf8db9f1867cb7d43516fff1
Co-authored-by: Caolán McNamara <caolanm@redhat.com>
Reviewed-on: https://gerrit.libreoffice.org/73548
Tested-by: Jenkins
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>