[Gentoo] X.Org modular tinderbox

Recently, anholt got the tinderbox working for modular X.

As the Pegasos that Genesi gave me holds the only place on the build page now, I encourage a few more people (especially those with interesting architectures) to jump on there. Just read the tinderbox page to get started. I recently ran a couple of days with a 2.4 kernel sparc, so that’s sort of covered. And daniels had an x86 and amd64 on there till recently, but they disappeared.