Draft: add cross build dependency satisfiability results from qa.debian.org/dose/debcheck

The Debian distro tracker now shows binary package and source package (build) dependency satisfaction problems. Here is another merge request which adds cross build dependency satisfaction problems to each source package suffering from them. This is how it looks like:

A similar request has been made for the Debian Maintainer Dashboard, albeit without a patch: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=929932

Helmut Grohne already has set up a cross buildd which regularly cross builds packages for all architectures and publishes build logs of failed cross builds. But the biggest blocker of cross-building more packages are still unsatisfied cross build dependencies. Here are some numbers:

• 30332 source packages are currently in Debian unstable
• of those, 14328 source packages build Architecture:any binary packages
• of those, 8037 source packages satisfy their cross build dependencies when building on amd64 for armhf (to pick an example architecture pair, the numbers for other architecture combinations are similar)
• of those, between 65% and 68% do successfully cross build on crossqa.debian.net

So while 56% of arch:any building source packages satisfy their cross build dependencies, 44% do not. If cross build dependencies can be satisfied, around two thirds of source packages do properly cross build in practice. This means that currently cross satisfiability issues are the biggest blocker holding back cross building efforts and thus I'd argue it would be useful to expose these problems to a wider audience via the distro tracker.

Additionally, it would make sense to first display cross build satisfiability results (this merge request) before showing actual cross building problems from crossqa.debian.net.