pmb.build.packages: always build abuild first if outdated

This fixes situations where abuild is outdated, and other outdated packages depend on the newer abuild. By always including it and moving it to the front of the queue, we make sure that subsequent outdated packages are always built with the latest abuild.

This (or something like this) is needed to fix the build failures in https://gitlab.com/postmarketOS/pmaports/-/merge_requests/5315