Cleaning up make clean's behavior

[Jeremiah]

As running make clean breaks the bootstrap script.
I propose we leverage git's shallow clones (git clone --depth 1 $URL)
and include the .git directory with the repo such that we could simply
have make clean check for git and if it exists run git clean -xdf and
then only if git fails to exist, fallback to the existing broken form;
which needs to be corrected.

per discussion with g_bor[m] about the default automake clean rules
being used currently; and per their suggestion bringing this question to
this distribution list for further discussion.

Additional wouldn't one want to pack the .git in the tarball to enable a
simplified update method.

jlicht pointed out that this would not be a problem yet for guix, but it
 does seem unconventional. It would not make sense for some bigger-repo 
projects (e.g. emacs) for sure though

Given that discussion background does anyone have any problems, concerns
or issues with the change proposed?