[clang] [Clang] Make passing incomplete types to builtin type-traits a non-sfinae-friendly error (PR #121333)

[Nikolas Klauser via cfe-commits]

https://github.com/philnik777 approved this pull request.

I think this is the right direction, so LGTM, but maybe you want to wait for other people to comment before landing.

https://github.com/llvm/llvm-project/pull/121333