sysexits: Tidy deprecated header and manual

<sysexits.h> was deprecated in the base system in a1432b4 for FreeBSD
8.0 and is retained only for backwards compatibility. Make that clear,
since sysexits(3) suggested using it since it was in style(9) prior
to this.

MFC after: 1 week
Co-authored-by: imp
Fixes: a1432b4
Reviewed by: imp, pauamma (previous version)
Pull Request https://github.com/freebsd/freebsd-src/pull/1195

include: Remove ancient SCCS tags.

Remove ancient SCCS tags from the tree, automated scripting, with two
minor fixup to keep things compiling. All the common forms in the tree
were removed with a perl script.

Sponsored by: Netflix

Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

include: further adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 3-Clause license.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.

Special thanks to Wind River for providing access to "The Duke of
Highlander" tool: an older (2014) run over FreeBSD tree was useful as a
starting point.

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.

Remove the Berkeley clause 3's.
Add a few $FreeBSD$

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

BSD 4.4 Lite Include Sources