ObjectiveC migrator. Another alternative to
 "atomic" or "nonatomic" for properties is
NS_NONATOMIC_IOSONLY. Use it if available.
// rdar://15442742


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@194503 91177308-0d34-0410-b5e6-96231b3b80d8