[plt-scheme] 3m platform support

Hi!

I'm doing a little bit on investigation because I am curious why the
current DrScheme has not entered Debian testing yet. You can see it's
status on <http://packages.qa.debian.org/d/drscheme.html>, telling that
it's blocken because there are no packages for alpha, hppa, mips,
mipsel, powerpc and sparc yet. Looking harder one can find 
<http://release.debian.org/migration/testing.pl?package=drscheme> which
lists the arches and it's builds which were failing lately. One can see
the failure message, the same problem that is described here:
<http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=473212>. As far I see
mzdyn3m.o is not being built on these platforms and causes the builds
to fail and therefore blocks the whole package from inclusion.

It would be fine to have a more recent version of DrScheme in Lenny, so
I'd be interested in cleaning this up. My question is now: does 3m work
on these arches at all? If not, the build has to be changed to use
another GC (on these or even on all arches, I don't really know, since
I am not a Debian Developer myself), so it can be built cleanly.

regards,
Marek