Hi guix!

this small series updates coq to the latest version. I had to update
zarith and a few dependencies (some of which cannot be updated
independently of coq), and fix the installation of lablgtk.

This version of coq uses dune, and I split the coq package into coq,
coq-ide-server (contains coqidetop) and coq-ide (contains the graphical
interface). This also simplifies the dependency graph for coq packages,
as they no longer need the graphical stack.

I tried building the documentation too, but it complains about missing
coq package, even if I added it to the inputs of coq-doc, so it's not
part of this series.