setup: move cffi stuff to mercurial/cffi...
setup: move cffi stuff to mercurial/cffi
This patch moves all setup*cffi stuff to mercurial/cffi to make the root
directory cleaner. The idea was from mpm [1]:
> It seems like we could have a fair amount of cffi definitions, and
> cluttering the root directory (or mercurial/) with them is probably not
> a great long-term solution. We could probably add a cffi/ directory
> under mercurial/ to parallel pure/.
[1]:
https://www.mercurial-scm.org/pipermail/mercurial-devel/2016-July/086442.html