As discovered by ChenWJ and listed on cfe-dev, the error for Objective C return type ended up being wrong. This fixes that. Additionally, as a "while we're there", the other usages of this error and the usage of the FP above both use a FixItHint, so I'll add it here.
I couldn't come up with a condition where this would cause the compiler to do anything odd, so I don't really have a good testcase for it. If any of you do, please let me know and I can add that!