This patch adds the necessary kernel and stty code to support setting
the IUTF8 flag for ttys. It is the first of two patches that fix
backspace behaviour for UTF-8 encoded characters when in canonical mode.
Reported by: christos
Reviewed by: christos, imp
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D42066
(cherry picked from commit 128f63cedc)
Approved by: re (gjb)
Bojan Novković
ad8c7f909e