swift234

SILGen: Fix the protocol witness label mismatch problem a third way.

r11586 is still too weak to handle both a label and an abstraction change. Instead of trying to handle this case in the guts of the reabstraction machine, where it ends up breaking other things, pre-sanitize the witness and requirement types before feeding them in. This is gross, but the keyword overhaul will hopefully make this unnecessarily before long.

Swift SVN r11588