Fixed handling of Objective-C properties to ensure

that automatically generated setters/getters only
get added to a class after explicitly declared (or
synthesized) getters/setters had the chance to be
added.  This eliminates conflicts creating errors
of the form:

error: instance method '...' has incompatible result
types in different translation units ('X *' vs. 'id')

llvm-svn: 157956