libutil: move ftime to libutil

It seems that there are still some applications that use ftime(3)
(for example, science/siconos and sysutils/lcdproc). The issue
is that we don't build libcompat as a shared library anymore.
The easiest solution is to move it to libutil, until we
deprecate it for good.

This solution was proposed by kib@ in
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=257789.

PR: 257789
MFC after: 1 month
Reviewed by: kib (ages ago)
Differential Revision: https://reviews.freebsd.org/D39994