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.
Fix confusing machine verifier error.

The error reported the number of explicit operands,
but that isn't what is checked. In my case, this
resulted in the confusing errors

"Too few operands." followed shortly by
"8 operands expected, but 8 given."