bin: Automated cleanup of cdefs and other formatting

Apply the following automated changes to try to eliminate
no-longer-needed sys/cdefs.h includes as well as now-empty
blank lines in a row.

Remove /^#if.*\n#endif.*\n#include\s+<sys/cdefs.h>.*\n/
Remove /\n+#include\s+<sys/cdefs.h>.*\n+#if.*\n#endif.*\n+/
Remove /\n+#if.*\n#endif.*\n+/
Remove /^#if.*\n#endif.*\n/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/types.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/param.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/capsicum.h>/

Sponsored by: Netflix

Remove $FreeBSD$: one-line .c pattern

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

General 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.

Renumber copyright clause 4

Renumber cluase 4 to 3, per what everybody else did when BSD granted
them permission to remove clause 3. My insistance on keeping the same
numbering for legal reasons is too pedantic, so give up on that point.

Submitted by: Jan Schaumann <jschauma@stevens.edu>
Pull Request: https://github.com/freebsd/freebsd/pull/96

Make ``realpath'' behave like ``realpath .''.

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.

Enhance realpath(1) in a number of ways:

- Allow realpath to accept multiple paths on the command line.
- Add -q to suppress warnings if some paths can't be processed, and use
getopt(3) to process flags.
- Print the path being requested rather than a possibly partially
processed path when a failure occurs so that you can tell which of
several passed paths did fail.

MFC after: 1 week
PR: 112920
Submitted by: Ighighi <ighighi@gmail.com>

Remove clause 3 from the UCB licenses.

OK'ed by: imp, core

realpath(3) should use PATH_MAX instead of MAXPATHLEN according to POSIX.

This also reverts the PATH_MAX -> MAXPATHLEN part of
rev 1.3 of src/bin/realpath/realpath.c

Requested by: imp
Reviewed by: imp, bde

Remove undocumented behavior (return current work dir if no path
is given as argument) that is not present in 4-Stable.
It was introduced when realpath(1) was split out of pwd(1).
The removed behavior is provided by pwd(1).

Reviewed by: mike

- use MAXPATHLEN per realpath(3)
- use the problematic part of the path, instead of the argument,
when reporting an error.

Reviewed by: mike

Check the return value of getcwd() to avoid printf()ing a NULL. Mark
usage() as __dead2 to avoid a GCC warning.

Spotted by: keramida

Move the realpath(1) source into its own directory. Previously, it
shared sources with pwd(1).