Can't compile with GCC5
The build instructions should tell which compiler you need for building, especially since the chibios ergodox infinity doesn't compile with the same AtmelAVR toolset as the main repository.
I also tried with the GNU Tools ARM embedded 5.2 2015q4 toolset, but that gave an internal compiler error.
Finally I installed the Chibi Studio and used the 4.9 2015q3 toolset, which seems to work fine. However not tested on the real keyboard yet, as I haven't received it yet, but tomorrow I probably will.
I'm using gcc-arm-none-eabi 4.8.3 on ubuntu, I didn't confirm which toolchanin chibios requires, although. It seems to me work so far but I'll have to check some time when I update documents.
People who use AVR toolchain for this keyboard are clearly out of target audience we expect :D (at this time at least.)
https://answers.launchpad.net/gcc-arm-embedded/+question/280242
Chibi doesn't build with gcc 5 yet.