All the bootstrap.factor scripts in cpu/ are run by the bootstrap to
make boot images, but aren't used otherwise. So I think it's cleaner to
put them in one directory inside the bootstrap hierarchy.
We also need to save C ABI volatile registers before calling the signal handler in order to be able to reliably resume. Add signal-handler and leaf-signal-handler subprimitives to preserve volatile registers before invoking the signal handler C function.
Björn Lindqvist
Joe Groff
Doug Coleman