swift

4f5bbc18 - AST: Fix macCatalyst availability for synthesized declarations. (#70534)

AST: Fix macCatalyst availability for synthesized declarations. (#70534) The macCatalyst platform availability of a declaration may be inferred from the iOS platform availability of that declaration in the absence of an explicit macCatalyst availability attribute. This means that when inheriting macCatalyst platform availability, the explict iOS availability of an inner ancestor should take precedence over explicit macCatalyst availability of an outer ancestor. The algorithm that computes inferred availability attributes for synthesized declarations was treating macCatalyst and iOS as independent platforms, though, sometimes yielding inapproparite macCatalyst availability. Resolves rdar://107766644