[clang] [Clang] Add attribute for consteval builtin functions (PR #91894)

[via cfe-commits]

https://github.com/cor3ntin approved this pull request.

LGTM
As discussed offline with @erichkeane we don't have good way to test this change until the patch to add is_within_lifetime lands

https://github.com/llvm/llvm-project/pull/91894