I have Unity 3.5 and the newest version of Xcode. When I build, I get 32 linker errors for stuff it can’t find. After searching a bit around the forums, I have come to believe that the problem is AppController.mm . I haven’t edited this in any way, but my version of Unity and Xcode are incompatible. Could somebody upload a working AppController.mm? Any help is appreciated. Thanks in advance! 
Which 3.5? The newest is 3.5.6f4, I suggest upgrading to that first, if you already haven’t. It’s compatible with newest XCode.
Are you using third party plugins? They might be patching / bring old AppController.mm.
I was using Unity 3.5.5. I upgraded and everything works fine. Many thanks to the brilliant community for their quick and helpful replies!