[Bug c++/126962] valgrind error at cp/pt.cc:26161 in unify_pack_expansion

[dcb314 at hotmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126962

--- Comment #6 from David Binderman <dcb314 at hotmail dot com> ---
After 90 minutes of reduction, I have:

namespace {
template<typename >
    class reference_wrapper;
  template<typename _Tp, _Tp >
    struct integral_constant
    ;
  template<typename _Tp, _Tp >
    _Tp integral_constantvalue;
  template<bool __v>
    using __bool_constant = integral_constant<bool, __v>;
  template<bool, typename >
    struct enable_if
    ;
  template<bool _Cond, typename _Tp = void>
    using __enable_if_t = typename enable_if<_Cond, _Tp>::type;
  template<bool>
    struct __conditional
    ;
  template<bool _Cond>
    using __conditional_t
      = typename __conditional<_Cond>::type;
  namespace {}
  template<typename>
    struct __or_
    ;
  template<typename>
    struct __and_
    ;
  template<typename>
    struct remove_cv;
  template<typename >
    struct is_arithmetic
    ;
  template<typename >
    struct __is_array_known_bounds
    ;
  template<typename _Tp, typename>
    using __is_constructible_impl
      = __bool_constant<__is_constructible(_Tp)>;
  template<typename , typename... >
    struct decay
    ;
  template<typename >
    struct __strip_reference_wrapper
    ;
  template<typename _Tp>
    using __decay_t = typename decay<_Tp>::type;
  template<typename _Tp>
    using __decay_and_strip = __strip_reference_wrapper<__decay_t<_Tp>>;
  template<typename... _Cond>
    using _Require = __enable_if_t<__and_<_Cond...>::value>;
  template<typename... >
    struct common_type;
  template<typename >
    struct __success_type
    ;  template<typename>
    struct __common_type_fold;
  template<typename _Tp1, typename _Tp2, typename... _Rp>
    struct common_type<_Tp1, _Tp2, _Rp...>
    ;
}