swift234

IRGen: SIL protocol type value support.
Factor out the witness table initialization and projection logic from GenProto so that IRGenSIL can use it to implement the ProjectExistential and InitExistential instructions. Also map the CopyAddr and DestroyAddr instructions to value witness table calls so that value semantics on protocol values (and other address-only values) work. The added test compiles but doesn't run yet because invoking methods on a protocol value still requires implementing the ProtocolMethod instruction.

Swift SVN r3787