[experimental] Fix handling of ARCHES_{QEMU,LXC} and release 9.6.0-3

Andrea Bolognanirequested to merge
abologna/libvirt:fix-arches into debian/latest

This should address the build failures seen on hppa, m68k and sh4 with the latest upload.

The failure seen on ia64 is different and will have to be investigated separately.

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