[clang] [clang] Implement provisional wording for CWG2398 regarding packs (PR #90820)

[via cfe-commits]

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h-vetinari wrote:

> Note we are not implementing the solution Jason posted on the core mailing list, neither on the previous patch, as we have a better solution than current GCC on this, nor on this MR, as GCC implements no such workaround and still fails this test.

Sounds like should perhaps note that we are implementing our own resolution, until there's an update to the cwg issue that can be referred to?

https://github.com/llvm/llvm-project/pull/90820