You can set up gcc as a cross-compiler. You merely have to build it with the correct platform specified to "--target". But gcc is not enough. You need binutils, system headers of the target system, and you have to build all of the libraries you need for your target system. It's a lot of work, and it can be tricky the first time. But the basic idea is the same for all platforms, so you should be able to find some resources online to help you through it, even if you can't find anything written specifically for MacOS X. I'm not going to write you a walkthrough, but I'll try to answer specific questions if you have any.
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“When Juffo-Wup is complete when at last there is no Void, no Non when the Creators return then we can finally rest.”