pmb.build: ensure all specified packages are built with --force

When running build --force, if a later package is a dependency of an earlier package, it will be "visited" by the dependency resolver, erroneously causing it to be skipped when later in the session it's visited to force build. This is because previously visited packages are marked as such in a hashmap, but skip_already_built() assumes that a package which has been visited would have already been built.

Fix this by overriding skip_already_built() if doing a force build. This works because package dependencies are only built if the APKBUILD version is newer than the binary repo, even when --force is specified. So there is no risk of an infinite loop here.

Signed-off-by: Caleb Connolly caleb@postmarketos.org