[Bug c++/64455] A constexpr variable template can't be used with enable_if

["ville.voutilainen at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64455

--- Comment #2 from Ville Voutilainen <ville.voutilainen at gmail dot com> ---
Reduced to avoid using type_traits:

template<typename Type>
constexpr bool IsType = true;

template <bool b, class T> struct Test
{
};

template <class T>
struct Test<true, T>
{
        typedef T type;
};

template<class T>
struct X {
    typedef typename Test<IsType<T>,T>::type type;
};

int main()
{
   X<int>::type t;
}