Hello Guix,

This patch adds an ‘install-license-files’ phase to ‘gnu-build-system’
and to all the build systems that inherit from it.  It is a followup to
the discussion with Dave Love:

  https://lists.gnu.org/archive/html/guix-devel/2017-09/msg00097.html

It’s an improvement over what we have now, although it’s rudimentary: it
copies to share/doc/PACKAGE-VERSION any file from the top-level source
directory that matches a regexp.

Thoughts?

Ideally we could apply it in this ‘core-updates’ cycle if that’s fine
with you.

Thanks in advance,
Ludo’.