https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80265
--- Comment #14 from Pedro Alves <palves at redhat dot com> --- AFAIK, the "if constexpr()" proposal was sent back for more work [1], seems premature to support it, while I'd hope that the __builtin_constant_p approach would allow supporting constexpr char_traits in GCC7 (either 7.1 or some later point release). (I don't exactly see where's the contradiction, but I'm not a real GCC hacker.) [1] - https://botondballo.wordpress.com/2017/03/27/trip-report-c-standards-meeting-in-kona-february-2017/
