This struct contains various switches to system and it feels somewhat
safer to have the compiler reassure us that nowhere else changes it.
One field that is changed, writeout_error, is split out and passed as
another argument.
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>