[Bug libstdc++/107871] _Iter_sink:: _M_overflow missing some difference type casting

[hewillk at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107871

--- Comment #2 from 康桓瑋 <hewillk at gmail dot com> ---
This is just an example. So, are users not allowed to define integer-like class
types?