[clang] [Clang] Check constraints for an explicit instantiation of a member function (PR #104438)

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Sirraide wrote:

> do you mean something like https://godbolt.org/z/4s6YEcrfa ?

I see both our godbolt links have a typo, but yes, I meant `A<2>::f`.

https://github.com/llvm/llvm-project/pull/104438