Hi guix!

This patch splits mariadb into three parts: out (150 MB), lib (38 MB)
and dev (5 MB). This means that dependents now have a lighter closure.

For instance, python-mysqlclient lost its references to gcc, perl,
jemalloc and one zlib reference. It went from 537.2 MiB to only 230.4
MiB. qtbase went from ~1.3 GB to ~1.0 GB.

I've rebuilt most of these direct dependents without issues, so I don't
expect any issue with this patch. However, since qtbase is in the
dependency graph, there are ~500 packages that need to be rebuilt, so
this patch qualifies for staging.