I have a working offset-by-0x100 stage0 now.

With cross compiling and IMMEDIATE words, things get icky with stable
ABI references. For the same reason that EXIT, (br) and (br?) need to
stay at stable offsets, these word references will not have BIN(
properly applied at Inner core xcomp.

The solution for now is to adjust during EXECUTE, which is ugly and
inefficient, but I don't see a better solution right now.

Will be useful for assembling binaries for the TRS-80 which can't start
at addr 0.