swift

6615c39d - Take the IUO-ness of a parameter declaration into account in ranking.

Take the IUO-ness of a parameter declaration into account in ranking. Normally we wouldn't need this because we do not allow overloading by parameter optionality. In this case, though, we import two Objective-C methods that end up getting renamed to the same name in Swift, one of which has a nullability annotation and the other of which doesn't. Before IUOs were removed from the type system, we would have failed a subtype test when ranking overloads, but now that subtype test passes because we're comparing two optionals of the same type. So the change here is to compare the optionality of the parameters and reject cases where we are testing whether a plain optional is a subtype of something declared to be an IUO. Fixes rdar://problem/38719575. (cherry picked from commit 0959f0ce7d0a9c1ae77d7d7129f927c012bbdb16)