libvirt is too old for qemu in unstable

[wedens]

Currently, qemu version is 4.2.0 and libvirt is 5.4.0. As I've already mentioned here there are some incompatibilities between qemu >= 4.1 and libvirt < 5.6.0. In some cases it may significantly affect performace (e.g. typical windows vm with vfio).

The latest libvirt version is 6.0.0. So, I think it's time to upgrade.

Unfortunately, it seems that something has changed in libvirt build process and just changing version/hash in existing derivation is not enough.

/cc @fpletz @globin (libvirt maintainers)

[wedens]

Turns out Nix was adding --disable-dependency-tracking flag which caused weird build failures.

After adding dontAddDisableDepTrack = true and some other small tweaks, it builds.

I'll try to open a PR myself this week after I test it. I won't be able to test it on Darwin, though.

(apparently autotools will be replaced with meson soon in libvirt)

[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/nixos-20-03-beta/5935/22