swift234

IRGen: Statically load superclass metadata for non-resilient classes

We only need to indirectly load the superclass's metadata when the
superclass is resilient. For example, we may be calling a super method
inside an extension of a class we don't own. Otherwise, we can
immediately load the statically known superclass.

Adds a testing flag to force resilient super dispatch, since the
IRGen module resilience checks aren't fully implemented yet.

SIL -> IR tests added.

rdar://problem/22749732

Also fixes rdar://problem/23884670