[libc-commits] [libc] [libc] Make add_with_carry and sub_with_borrow constexpr. (PR #81898)

[Nick Desaulniers via libc-commits]

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

Neat, TIL about `__builtin_is_constant_evaluated`.

https://github.com/llvm/llvm-project/pull/81898