2. Immediate words that have been cross compiled *cannot* be
   used. Only immediates from the host system can be used.
3. If an immediate word compiles words, it can only be words
   that are part of the stable ABI.

All of this is because when cross compiling, all atom ref-
erences are offsetted to the target system and are thus
unusable directly. For the same reason, any reference to a word
in the host system will obviously be wrong in the target
system. More details in B260.

This unit is loaded in two "low" and "high" parts. The low part
is the biggest chunk and has the most definitions. The high
part is the "sensitive" chunk and contains "LITN", ":" and ";"
definitions which, once defined, kind of make any more defs
impossible.                                             (cont.)