https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64455
--- Comment #1 from Ville Voutilainen <ville.voutilainen at gmail dot com> ---
Btw, this problem prevents using the C++14 trait aliases with the forthcoming
trait variable templates as they were intended, because
template <class T> enable_if_t<is_same_v<T, int>> f() {}
is also erroneously rejected with the diagnostic that is_same_v<T, int>
is not usable in a constant expression.
