[Bug c++/118454] [15 regression] ICE when building scipy-1.15.1 (hash table checking failed: equal operator returns true for a pair of values with a different hash value)

[sjames at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118454

--- Comment #6 from Sam James <sjames at gcc dot gnu.org> ---
Reduced:
```
template <typename> struct complex_type;
template <typename T> using complex = T;
template <typename, long> class dual;
template <typename T, unsigned long... Orders>
void abs(dual<complex<T>, Orders...>);
template <typename T, unsigned long... Orders>
struct complex_type<dual<T, Orders...>>;
```