swift234

IRGen: Bind archetype metadata for generic value witnesses.

Use EmitPolymorphicParameters to extract the metadata for generic type parameters from the "self" argument to value witnesses so that they're available to the value witness implementation. This makes it so that the compiler no longer crashes when emitting the value witness table for a generic struct with dynamic size.

This temporarily breaks generic unions since we didn't properly implement generic argument lookup for union metadata yet. Fix coming shortly.

Swift SVN r7910