swift234

AST: Initial work to canonicalize generic signatures for mangling.

Currently GenericSignature::getCanonicalSignature isn't able to canonicalize the set of requirements due to fragile dependencies on generic signatures matching AllArchetypes order of their originating GenericParamLists. However, we shouldn't let that stop us from getting the mangling right, so implement a "getCanonicalManglingSignature" that builds the true canonical signature by feeding it into an ArchetypeBuilder and shedding unnecessary constraints. For now, just handle conformance and base class constraints; still to do are same-type constraints.

Swift SVN r28191