Compiling DMD for *nix platforms

[Leo Singer]

== Quote from Anders Bergh (anders1 at gmail.com)'s article

> You can't compile dmd because it's not 100% open source, only the
> frontend is. If you download the latest gdc code using svn then you
> can do something like this to enable D 2 support:
> ./gcc/d/setup-gcc --enable-d-language=2 (or so, I don't remember)

Sweet!  That's exactly what I want.
I've heard some rumors about using gcc's backends for other platforms to use D on embedded systems.
That's exactly why I'm interested in D.  What would need to be done to make a cross-compiler for <insert
favorite gcc backend here>?