swift234

SILGen: Propagate function thin-ness through specializations.

Now that we actually support generic protocol methods, we can end up specializing non-thin function values (because the protocol_method/archetype_method value carries the This metadata as payload), so the thin-ness of the specialized function type needs to be constrained by the input type's thinness. Relax the verifier to allow a specialize inst to produce a thick value if its input is thick.

Swift SVN r6598