Are you using Xcode 2.5? 

OK, that's my problem: I'm on Xcode 3.2.1 (with iPhone SDK 2.1 installed).

Latest Xcode version support would be great, so we could try out all the awesomeness that's provided by Clang.

Anyway, I'm excited about having MAME OS X back with support for the latest MAME version. Thanks a lot for your continued effort!