testing/guix: new aport

Guix is a functional package manager (similar to testing/nix), it can be used for all kinds of purposes. I am specifically interested in using it as a tool for reproducible research. Requires some patches to work well with musl, should hopefully be upstreamable. Also adds a handful of dependencies as we don't have a lot of Guile packages right now.

More information: https://guix.gnu.org