Most of the gcc source distributions will build fine on a mac; I didn't have any trouble using darwinports to install gcc-elf-m68k, for instance (which is supposed to support coldfire.) But I have my confusions about just which versions of gcc support which versions of coldfire (see my post on towergeeks), and installing binaries from vendors like codesourcery is another matter. I've been playing with VMWARE and Parallels (so far I like VMWare better. It even almost runs W98. Now all I need is a WXP install disk that isn't bound to a particular vendor. I have plenty of machines with WXP license stickers that aren't running WXP any more, which I would consider morally sufficient to "transfer" the license. Sigh. But all my actual WXP disks are "system restore" disks for particular vendor systems rather than "install" disks.)
Check out this "tower to shield" converter (not quite done yet!):