[Bug libstdc++/81806] Split in pbds works in O(n) instead of O(log n)

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81806

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Feedback was provided: https://gcc.gnu.org/ml/gcc/2019-07/msg00082.html