Makes xcomp.fs units shorter.

TODO: implement X['] so that I can remove those XCURRENT patterns.

This leaves space for xcomp-core which is growing.

This allows us to move words like ABORT" to xcomp-core, which is
I think the last roadblock before being able to unify all drivers
into a single xcomp layer.

Now I struggle to remember why I ever did things they way I did.
There must have been a reason...

The goal is to insert device drivers in between.

I'd like to move this code, along with all recipe contents, to blk/.
It's easier if "emul-related" code is gathered at the same place.

With all this recent movements, we had a bit of a fragmentation
issue.

I'm reserving the 100-200 range for non-bootstrapping needs.

no floppy yet.

Big bootstrapping change which greatly reduces the role of the modern
operating system in the bootstrapping process.

Less noisy this way

The way is clear for complete stage1 bootstrapping on the RC2014
target!

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).

We can now cross-compile core.fs.

Memory mapping is a dead end too, solution has to be at a higher
level. xcomp is my new approach.