Downloaded the source as soon as I discovered orx and tried to compile it. Few problems here and there but I fixed them! Mostly it was -isysroot was wrong for 10.9. First I set it to the correct one but then I found simply removing the option from premake4.lua worked too. Also glext.h had a conflicting typedef with the system OpenGL.framework.
Not sure if this is the right way to fix things, but here's a patch:
Most of the patch is actually due to the premake4.lua changing the output gmake Makefiles (they could probably be removed from the hg repos since they should be generated locally anyway...).
Good work on orx, code looks really neat!