[Bug c++/66743] ICE on formerly working code

[webrown.cpp at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66743

--- Comment #1 from W E Brown <webrown.cpp at gmail dot com> ---
Further reduced test case:

template< class T >
  using u_t = __underlying_type(T);

int  main( )  { }