match our import of the (un)vis(3) APIs.
This adds support for multibyte encoding and the -h and -m flags which
support HTTP and MIME encoding respectively.
PR: bin/175418
Obtained from: NetBSD
of the recent WARNS commits. The idea is:
1) FreeBSD id tags should follow vendor tags.
2) Vendor tags should not be compiled (though copyrights probably should).
3) There should be no blank line between including cdefs and __FBSDIF.
