Are you getting a clang error that you can't track down? "What the heck is 'clang: error: '-I-' not supported, please use -iquote instead'!?!" Oh compiler gods please help this poor soul. Well hopefully you haven't burned a day trying to solve this by tracking down project includes, compiler versions, and lord knows what else. The answer turns out to be head-slappingly easy, you've got an unsupported character somewhere in the project path. In our case we had something like this:
/Users/joeblow/Devel/Projects/WARU - Joe/testDir/waru/WARU.xcodeporj
[whitespace]
Notice the hyphen in there, that was the cause of all the pain. The fix was simply to remove the hyphen:
/Users/timwmartin/Devel/Projects/WARU/testDir/waru/WARU.xcodeporj
[whitespace]
Hope this helps someone out there!