I made the mistake of using an earlier Xcode project file that I had already changed. When I downloaded the code again, regenerated the Xcode project file and attempted to compile it, I received a compilation error. The error said that Main_RequestQuit did not have the proper number of parameters. In every other instance except PrefsController.m, the call said Main_RequestQuit(0). It was simply Main_RequestQuit() in PrefsController. It appears this function changed from returning void to returning an integer value.
I changed PrefsController.m to return 0 and Hatari compiled again.