ObjectiveC migration: tweak setting of lifetime attribute
on @property migration. Don't set unsafe_unretained
on non-object properties. Set 'retain' on strong
properties. Makecertain properties with specific
names unsafe_unretained as well.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@187810 91177308-0d34-0410-b5e6-96231b3b80d8