HPC: switch to shared Guix from “guix pull”

[Ricardo Wurmus]

Hi,

in the HPC setup at the MDC, we have a shared Guix installation, which
provides the daemon and a reasonably recent “guix” command, which should
be enough to let people run “guix pull”.  This Guix installation is
really just a configured and built git checkout, and the “guix-daemon”
is started with “./pre-inst-env guix-daemon” in a suitable environment.

This is ugly, so I’d like to switch to “guix pull”, which provides both
the daemon and the “guix” command.

For historical reasons, Guix here is configured with
localstatedir=/gnu/var instead of just /var.  “guix pull”, however,
provides a Guix that is configured with “localstatedir=/var”.

How can I override this?

--
Ricardo