ssh: fix SIZEOF_TIME_T #define on i386

Reported by: imp
Reviewed by: imp
MFC after: 3 days
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D38443

(cherry picked from commit 1aa9a35f6361cc898e2323e1f2823771eb4161da)
(cherry picked from commit 59ab4b95129dd5d64a52e0822b4fb5621bf65e9c)