[arc] When merging ImmutablePointerSets, since they are uniqued, we can bail early on merging the same set by just performing a pointer equality.
[arc] When merging ImmutablePointerSets, since they are uniqued, we can bail early on merging the same set by just performing a pointer equality.

Just a drive by I noticed. Should improve compile time.

khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift