gnome-base/gconf-1.0.8-r4 specifies a dependency of >=sys-libs/db-3.2, but it only builds with db3, not db4. It does continue the build process though disabling db support if only db4 is present.
i dont think the db backend is used or stable, it can probably go. We can't force it to be disabled easily, so i just removed the dep. That should suffice. Fixed this in all 1.0* revisions, but r5 contains some minor additional fixes, so arches CC-ed please test and mark gnome-base/gconf-1.0.8-r5 stable as well so the older revisions can be removed. Alpha got marked stable by accident i think, but please also make sure it works correctly.