Tweak the type lowering code to work when the conforming type is generic. Handle the case of an associated type with protocol requirements being witnessed by an archetype of the conforming type, which results in a null ProtocolConformance pointer in the witnessing substitution.
Swift SVN r11275
When a type conforms to a protocol that refines another protocol, emit the witness table for the base protocol, and drop a reference into the witness table for the derived protocol. Keep track of what conformances we've already emitted so we don't emit redundant witness tables when types conform redundantly to base protocols or have multiple references to a base protocol via a refinement diamond.
Swift SVN r11263
Walk the ProtocolConformances of type and extension decls to produce SILWitnessTables for them. Work out the type of the witness function by applying substitutions from the witness map and lowering it at the abstraction level of the requirement, then emit a symbol for the witness function (but don't emit the body of the witness function just yet).
Swift SVN r11143
We will generate these in SILGen when we see a NormalProtocolConformance, to provide a mapping of method requirements to witnesses for types.
Swift SVN r10900
