Cross compilation program

This programs allows cross compilation of boot binary and
icore. Run "262 LOAD" right before your cross compilation and
then set XCURRENT to CURRENT and XCOFF to H@.

This redefines defining words to achieve cross compilation.
The goal is two-fold:

1. Add an offset to all word references in definitions.
2. Don't shadow important words we need right now.

Words overrides like ":", "IMMEDIATE" and "CODE" are not
automatically shadowed to allow the harmless inclusion of
this unit. This shadowing has to take place in your xcomp
configuration.                                          (cont.)