https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86862
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Reduced testcase:
```
namespace std {
template <typename _CharT> struct char_traits {};
}
template <class Char, template <class> class Traits>
struct b { virtual ~b(); };
template <class Char>
struct d : public b<Char, std::char_traits> {};
extern template class d<char>;
```
Note `std::char_traits` needs to be exactly that; otherwise the ICE does not
show up.
