Add a new "BuildDependsPolicy" that will check the satisfiability of
the build-dependencies listed in the Build-Depends and
Build-Depends-Arch fields. This enables gating of packages based on
missing / broken build-dependencies.
There are some limitations:
* Build-Depends-Indep is ignored for now. Missing or broken packages
listed in Build-Depends-Indep will be continue to be silently
ignored.
* Being a policy check, it does not enforce "self-containedness" as
a package can still migrate before a build-dependency. However,
this can only happen if the build-dependency is ready to migrate
itself. If the build-dependency is not ready (e.g. new RC bugs),
then packages build-depending on it cannot migrate either (unless
the version in testing satisfies there requirements).
Signed-off-by: Niels Thykier <niels@thykier.net>
