swift

6c64636f - [Clang importer] Infer @_downgrade_exhaustivity_check for new-to-2017 enum elements in Swift 3.

[Clang importer] Infer @_downgrade_exhaustivity_check for new-to-2017 enum elements in Swift 3. In Swift 3 mode, infer @_downgrade_exhaustivity_check for any enum elements that were introduced in the 2017 SDKs (macOS 10.13, iOS 11.0, tvOS 11.0, watchOS 4.0). This is a stop-gap until we get "open" enums, but serves an important source-compatibility use case. Fixes rdar://problem/32824207. (cherry picked from commit f855d2f87edd9c919ba73e78061c162d988d86f1) (cherry picked from commit f72b8e5c209a9d578d51aacd59dc585849a585c6)