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
Rewrite the handling for the `CxxStdlib` implicit linking to use a
slightly more functional style for filtering. Additionally, add Windows
to the list providing the overlay. The Windows linking scenario is a
slightly more complicated as the library names differ between static and
dynamic variants to disambiguate between import libraries and static
libraries. Take this into account when embedding the library name so
that the linker can find the appropriate content.
In libc++, `pair()` and `pair(_T1 const& __t1, _T2 const& __t2)` are templated with `enable_if`, so these initializers are not imported into Swift.
There should be a way to call `std.pair.init` from Swift, so this change makes sure Swift synthesizes a memberwise initializer for `std.pair`.
rdar://113135110
This disables TBD validation when C++ interop is enabled, unless an explicit `-validate-tbd-against-ir=` flag was passed.
rdar://83405989 / https://github.com/apple/swift/issues/56458
