27.5.1.3.13 operator== [reverse.iter.op==]
template<class Iterator1, class Iterator2>
constexpr bool operator==
( const reverse_iterator<Iterator1>& x,
const reverse_iterator<Iterator2>& y);
1 Returns: x.current == y.current.
1 Returns: x.base() == y.base().
1 Returns: x.current == y.current.