swift

a0ab1dc4 - [Frontend] Add `ExtensibleAttribute` to guard use of `@extensible` attribute

[Frontend] Add `ExtensibleAttribute` to guard use of `@extensible` attribute Guard against condfails when older compilers get a swift interface that uses `@extensible` attribute. The attribute itself doesn't have any effect in swift interfaces yet since all of the public enums are already resilient in that mode. (cherry picked from commit 6d89bca76501812a8813bd79a8e48b6bc1debd4a)