[Bug c++/80265] __builtin_{memcmp,memchr,strlen} are not usable in constexpr functions

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80265

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
That doesn't work in this case:

constexpr bool str()
{
  char s[] = "str";
  return ce_char_traits<char>::length(s) == 3;
}

static_assert( str() );

i.e. it works OK for C++11-style constant expressions, but not C++14 ones.