swift

fe138e01 - AST: Track an unavailable domain instead of platform in AvailabilityContext.

AST: Track an unavailable domain instead of platform in AvailabilityContext. Now that most of the compiler tracks availability in terms of AvailabilityDomain, it's time to do so in AvailabilityContext as well. This will ensure that the compiler accurately suppresses diagnostics about a decl being unavailable in an arbitrary domain when the context of the use is already unavailable in that domain. With this change, most of the special-casing for the Embedded Swift availability domain has been removed from the compiler, outside of parsing and interface printing.