[clang] [Clang] SFINAE on mismatching pack length during constraint satisfaction checking (PR #101879)

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

> The intent is for this to be backported to 19 (therefore no changelog)

Yes, this is very important to backport.

https://github.com/llvm/llvm-project/pull/101879