In the debian package there is a patch for HURD, that basically does nothing:
http://patch-tracker.debian.org/patch/series/view/libdiscid/0.2.2-1/hurd.patch

This is nonsense in "it is not actually HURD-dependent". We could do that for every "unsupported" system.
With discid_put(), libdiscid is still of use (although most people would want discid_read()).

We don't need to add a non-empty default device if we are not going to read it anyways.

We should try at least to add BSD variants in the cmake build before that.