[Bug c++/70816] bogus error __builtin_strcmp is not a constant expression in a constexpr function

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70816

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Our std::char_traits has similar branches for constant evaluation (and the rest
of the library does too for memcpy etc.)