[Bug c++/87699] Implement CWG 1512

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87699

--- Comment #6 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
See Daniel's testcase for why this is more important than it might seem:

template<class T, decltype((((T*) 0) < nullptr), true) = false>
bool test(T*)
{
  return true;
}

int main()
{
  test((int*)(nullptr));
}