[clang] [Clang] Implement C++26’s P2893R3 ‘Variadic friends’ (PR #101448)

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

> I think the dr test already say "Clang 20 implements 2024-07-30 resolution" which is correct

While I understand what you're referring to (author's claim that the example is nonsense and should be rejected), if you open https://cplusplus.github.io/CWG/issues/2917.html, the only resolution there is dated 2024-08-16.

If for whatever reason we think that we should stick to that instead of considering newer proposed resolution, I'm happy with a simple replacement of `open` with `review` in the status.

https://github.com/llvm/llvm-project/pull/101448