https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84297
--- Comment #2 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Reduced, hopefully still valid. But clang++ accepts it.
struct integral_constant {};
template <bool> using __bool_constant = integral_constant;
template <typename _Tp, typename... _Args>
struct A : __bool_constant < __is_trivially_constructible(_Tp, _Args...)>
{};
A<int, int &()> a;
Started with r226381.
