For architectures where time_t is wide enough, in particular, 64bit
platforms, avoid overflow after year 2038 in clock_ct_to_ts().

PR:	195868
Reviewed by:	bde
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week


git-svn-id: svn+ssh://svn.freebsd.org/base/head@275727 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f