swift

e72af26d - [cherry-pick release/6.0.0][Sema] Allow unrecognized platforms in @backDeployed and @_originallyDefinedIn

[cherry-pick release/6.0.0][Sema] Allow unrecognized platforms in @backDeployed and @_originallyDefinedIn Don't emit attr_availability_need_platform_version for a @backDeployed or @_originallyDefinedIn that have a single unrecognized platform name. rdar://134207783