[Bug c++/108550] the type 'const auto' of 'constexpr' variable is not literal

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108550

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Slightly reduced:
```
#include <type_traits>

struct unique_ptr
{
    int operator->(){return true;};
};

template <class Tp>
constexpr auto is_pointer_v = std::is_pointer<Tp>::value;

template <class Tp, int* = nullptr>
auto Wrap1(int) -> std::integral_constant<bool,
is_pointer_v<decltype(Tp{}.operator->())>>;

template <class Tp>
auto Wrap1(...) -> std::is_pointer<Tp>;

int main() {
  static_assert(!decltype(Wrap1<unique_ptr>(0))::value); // error
  return 0;
}
```