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

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Sirraide wrote:

Pretty sure it did yeah; the change is that this case is now no longer valid: https://github.com/llvm/llvm-project/pull/101448#issuecomment-2304770725

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