objective-C: When implementing custom accessor method for
a property, the -Wdirect-ivar-access should not warn when 
accessing the property's synthesized instance variable.
// rdar://13142820


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@175195 91177308-0d34-0410-b5e6-96231b3b80d8