Show NonsolvableDepsInExp if Prefix is mentioned

[thesamesam]

Sometimes it's useful to do Nattka chasing on a bug, but this isn't possible right now for Prefix.

The gist is that Nattka could/should? act normally but include NonsolvableDepsInExp if prefix@ is in CC and/or prefix keywords (let's just assume ~*-linux and such, but it's mostly going to be the CC that does it...) are used.

Original report in Gentoo is here.

[thesamesam]

Actually, thinking about it, given nattka isn't concerned with cleanups and such, should we really be ignoring exp at all? If we mention them in a bug, we want the sanity check green?

We could always add an extra Bugzilla field to ignore exp arches if needed.

[mgorny]

Well, Prefix probably won't work if they're still relying on their overlay.

The big problem with "exp" is that every time a bug involves an exp arch, all other arches would be blocked by possibly large unsolved deptrees.