Objective-C: Tighten the rules when warning
is issused for on overriding 'readwrite'
property which is not auto-synthesized.
Buttom line is that if hueristics determine
that there will be a user implemented setter,
no warning will be issued. // rdar://13388503


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@177662 91177308-0d34-0410-b5e6-96231b3b80d8