swift-6
swift-5.9
This gives projects using C++ interop compat mode 5.9 access to the new features such as virtual methods and move-only types. rdar://126485814
Clang is using C++17 standard version by default since Clang 16. Swift’s ClangImporter should do the same, to make sure that clients who run clang and then swiftc without explicit std version see consistent behavior. rdar://125777068