ObjectiveC ARC. Lookup type associated with objc_bridage at
the point of CF object type-cast and issue diagnostic
if it is not a valid ObjectiveC class. // rdar//15454846.
This is wip.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@194861 91177308-0d34-0410-b5e6-96231b3b80d8