Cross compilation program

This programs allows cross compilation of boot binary and
icore. Run "262 LOAD" right before your cross compilation and
then "270 LOAD" to apply xcomp overrides.

This unit depends on a properly initialized z80a with ORG and
BIN( set. That is how we determine compilation offsets.

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.

                                                        (cont.)
