Pattern matching on newtype structs doesn't work cross crate

[pcwalton]

How embarrassing.

[luqmana]

I have a patch which fixes this by just adding def_fn to a few match patterns but it seems a bit hacky. I'm not sure why resolve treats newtype structs as def_fn instead of def_struct as it does when not cross crate.

[luqmana]

Fixed by #6121.