x11-themes/gtk-arc-themes: Try to fix build order bug (D29353)
Uncovered while building with devel/samurai but can probably also
happen with ninja eventually.
samu: job failed: /usr/local/bin/glib-compile-resources --sourcedir=common/gtk-3.0 --target=common/gtk-3.0/gtk-lighter.gresource common/gtk-3.0/gtk-lighter.gresource.xml
common/gtk-3.0/gtk-lighter.gresource.xml: Failed to locate checkbox-checked.png
PR: 254678