pmb/build/package: build depends of subpackages
Make sure that we build depends of subpackages, to avoid errors like the following:
- postmarketos-base has a subpackage postmarketos-base-nftables, which depends on postmarketos-config-nftables
- when pmbootstrap builds postmarketos-base with all its dependencies, it did not realize it depends on postmarketos-config-nftables through the subpackage, but it built it anyway
- when trying to install postmarketos-base-nftables, apk complains that there is no postmarketos-config-nftables:
ERROR: unable to select packages:
postmarketos-config-nftables (no such package):
required by: postmarketos-base-nftables-32-r2[postmarketos-config-nftables]
This also adds the missing depenendencies to "pmbootstrap repo_missing", which bpo uses to resolve dependencies.
Fixes #2084