[RFC:util/macros] Add XORG_CHECK_GROFF for building specs

[Matthieu Herrb]

Alan Coopersmith wrote:
> Thanks, I like this idea, and wish it had been done before I moved
> all those troff docs from xorg-docs to the individual modules (though
> there's still more to move out of xorg-docs).
> 
I like that too, and I'd even also like to see the same kind of macro
for XMLTO. As a distro maintainer I'd like to be able to control which
version of xmlto (or groff) is used by the build, and -- more important
-- disable xmlto completely because, since the base system doesn't
provide it so I need to be able to produce reproducable builds, even if
some users have installed something called xmlto in their path.

-- 
Matthieu Herrb