objective-C: Don't warn of unimplemented property of protocols in

category, when those properties will be implemented in category's 
primary class or one of its super classes. // rdar://12568064


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@170573 91177308-0d34-0410-b5e6-96231b3b80d8