MFC r317034:

Fix strcoll_l disagreeing with strxfrm by reworking the forward order case in
wcscoll_l().

Illumos fixed this while grabbing back our patches:
https://www.illumos.org/rb/r/402/

This does not 100% fix what postgresql folks reported as there is still a
remaining issue: https://www.illumos.org/issues/7962, it improves the situation

The initial issue was reported in postgresql mailing lists:
https://www.postgresql.org/message-id/flat/111D0E27-A8F3-4A84-A4E0-B0FB703863DF@s24.com#111D0E27-A8F3-4A84-A4E0-B0FB703863DF@s24.com

Submitted by: Yuri Pankov <yuri.pankov@nexenta.com>
Obtained from: Illumos