Currently, `make` is the same as `make bc`, but the idea is that
`make` can become the same as `make cs` when some other pieces are in
place.
The source of the top-level makefile is now ".makefile", and it's
turned into "Makefile" using "racket/src/makemake.rkt". The
transformation makes non-GNU `make` variants and `nmake` act like GNU
make to propagate variables, which makes abstraction through targets
plus variables (admitedly an abuse of `make`) more reliable and
consistent.
Why abuse `make` this way? Because `make` variants and `nmake` are
similar enough that to constitute a portable scripting language, and
one that conveniently provides a large number of entry points.
Also, schemified "thread", "io", "regexp", "schemify", and "expander"
layers are checked in. Overall, building Racket CS no longer requires
first building Racket BC.
