IBOutlet and weak attributes when accessed being
unpredictably set to nil because usage of such properties
are always single threaded and its ivar cannot be set
to nil asynchronously. // rdar://15885642 


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@211132 91177308-0d34-0410-b5e6-96231b3b80d8