Cross-compiling on Linux for OSX using osxcross
Good news everyone!
Note that not all packages support this (but most do). Most notably, I ran into a gcc bug while trying to build 32bit binaries for LuaJIT on an x64 Ubuntu 14.
If you use this, please report any problems. I will build all binaries using this method and test them on my Mac when I find the time (I'm pretty short on time till next year but I can scrape an hour or two here and there).
Also related: I downgraded my Mac to OSX 10.7 so that I can catch any backwards-compatibility problems while developing (can still dual-boot to 10.9). I can't say I see much difference betwen 10.7 and 10.9 anyway so nothing is lost :)
Btw, this is one step in the direction of building a cross-platform CI system. The next thing to try is to cross-compile for Windows using mingw-w64 and after that, (oh the irony) the hardest of all: compiling for Linux using Ubuntu 10 on Docker maybe... or something.