This would allow things like temporary giving control to the *CL
line on the TRS-80. For example... A very far fetched example. Not
at all the only *raison d'etre* of the layer...
It seems that xcomp can't manage to reliably compile core+ units.
Let's limit the role of xcomp to z80c+icore.
I'm getting a little desperate here. I'll revisit the link.fs approach
with a new idea I had...
... instead of building boot.fs, and then z80c.fs/icore.fs in separate
passes. This strengten xcomp by making it support 2 completely separate
dicts (that is, the X dict is *not* connected to the system dict. The chain
now stops at EXIT def in boot.fs).