See http://gdcmac.sourceforge.net/ and
http://sourceforge.net/projects/gdcmac/

* gdc-0.11-mac-10.3.dmg (Panther package)
* gdc-0.11-mac-10.4.dmg (Tiger package)

Installs under /opt/gdc, links with
the regular system compiler GCC 3.3.

--anders