https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80265
--- Comment #38 from Jonathan Wakely <redi at gcc dot gnu.org> --- char_traits<wchar_t> now uses either __builtin_constant_p or __builtin_is_constant_evaluated to avoid using wcslen in constant expressions. If that isn't working with clang for some reason that's a separate issue (and maybe something clang needs to fix, e.g. by implementing __builtin_is_constant_evaluated).
