[ARC] When casting from a pointer to an objective-c object with known ownership, if the

cast type has no ownership specified, implicitly "transfer" the ownership of the cast'ed type
to the cast type:

id x;
static_cast<NSString**>(&x); // Casting as (__strong NSString**).

This currently only works for C++ named casts, C casts to follow.

llvm-svn: 134273