Comment 4 for bug 1841066

And this makes sense, when porting the libvirt part we have seen it relies on unavailable-features, but I'd back then thought that would be via query-cpu-definitions.
But obviously (as libvirt will use QOM) it needs it here.

So our qemu in Eoan (and our arch_capability backports) lack this change (and maybe some context) to make qemu able to talk with libvirt about the arch-capability features correctly.

I'm going to try identifying what we need in Eoan on top on what we have.