Merge branch 'cross-compile-revamp' into blead

Merge branch 'cross-compile-revamp' into blead

This branch modifies how the cross-compilation model works.

The main change is that we now build a host miniperl to use locally,
rather than running each call to miniperl remotely.

It also removes several of the exceptions from the old model (no xlib,
xconfig.h, or Cross.pm).