The speed of the whole build process can be improved significantly by the
addition of an asynchrous cvs update and build process.  Do the checkouts
in another thread while the compile proceeds in the foreground.  Very
simple thread synchronization would be required to ensure that the build
thread doesn't start building a module until it has finished checking it out.

A work around that currently acheives most of this is to run a jhbuild
update in one terminal, wait until libxml finished checking out, then run a
jhbuild build -an in another terminal.