Removing the need for ./configure --localstatedir=/var ?

[Christopher Allan Webber]

Every now and then I rebuild Guix and hit the problem where I run
./configure and then I am reminded that I need to instead do:

  ./configure --localstatedir=/var

IIRC this is because of GNU standards about default paths and pretty
much no other reason that we don't default to /var.  But I think Guix is
a special case.

Should we ask maybe for an exception?  There's no reason for users to
bump into this.  It's annoying even for me, and at least I know (or
think I do) why.

 - Chris