libc: Purge unneeded cdefs.h

These sys/cdefs.h are not needed. Purge them. They are mostly left-over
from the $FreeBSD$ removal. A few in libc are still required for macros
that cdefs.h defines. Keep those.

Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D42385

Remove $FreeBSD$: one-line .c pattern

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

if_indextoname(3): Correct the RFC in a comment

RFC 2533 refers to 'A Syntax for Describing Media Feature Sets',
which is wrong since the correct reference should be
RFC 2553 'Basic Socket Interface Extensions for IPv6'.

Obtained from: OpenBSD
MFC after: 1 week

libc: Shortcut if_indextoname() if index == 0

If the index we're trying to convert is 0 we can avoid a potentially
expensive call to getifaddrs(). No interface has an ifindex of zero, so
we can handle this as an error: set the errno to ENXIO and return NULL.

Submitted by: Nick Rogers
Reviewed by: lutz at donnerhacke.de
MFC after: 2 weeks
Sponsored by: RG Nets
Differential Revision: https://reviews.freebsd.org/D24524

SPDX: mostly fixes to previous changes.

Introduce the recently approved BSD-1-Clause and replace 0BSD which
never did fit well our use cases.

Use the LLINDEX macro to access the link-level I/F index. This makes
it possible to work with a different type for the sdl_index field --
it only requires a recompile.

Obtained from: Juniper Networks, Inc.

A new jail(8) with a configuration file, to replace the work currently done
by /etc/rc.d/jail.

Create the altix project branch. The altix project will add support
for the SGI Altix 350 to FreeBSD/ia64. The hardware used for porting
is a two-module system, consisting of a base compute module and a
CPU expansion module. SGI's NUMAFlex architecture can be an excellent
platform to test CPU affinity and NUMA-aware features in FreeBSD.

- Import the HEAD csup code which is the basis for the cvsmode work.

Use BSDi derived if_nametoindex(), if_indextoname(), if_nameindex()
and if_freenameindex().

Obtained from: KAME
MFC after: 2 weeks