swift

9cadb9df - [ClangImporter] Update AvailAttr import for "macosx" to "macos" rename.

[ClangImporter] Update AvailAttr import for "macosx" to "macos" rename. This resolves a number of failing tests caused by availability attributes not getting imported for macOS. (cherry picked from commit e0489d356a9683c444a118f490949aabd18adb0c) Reapply this cherry-pick; it was accidentally reverted as part of f4d68f6.