Remove $FreeBSD$: two-line .h pattern

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

Mark usage function as __dead2 in programs where it does not return

In most cases, usage does not return, so mark them as __dead2. For the
cases where they do return, they have not been marked __dead2.

Reviewed by: imp
Pull Request: https://github.com/freebsd/freebsd-src/pull/735

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.

Use nitems() from sys/param.h.

MFC after: 4 weeks.

Stop including if_var.h from userland.

Sponsored by: Nginx, Inc.

More -Wmissing-variable-declarations fixes.

In addition to adding `static' where possible:

- bin/date: Move `retval' into extern.h to make it visible to date.c.
- bin/ed: Move globally used variables into ed.h.
- sbin/camcontrol: Move `verbose' into camcontrol.h and fix shadow warnings.
- usr.bin/calendar: Remove unneeded variables.
- usr.bin/chat: Make `line' local instead of global.
- usr.bin/elfdump: Comment out unneeded function.
- usr.bin/rlogin: Use _Noreturn instead of __dead2.
- usr.bin/tset: Pull `Ospeed' into extern.h.
- usr.sbin/mfiutil: Put global variables in mfiutil.h.
- usr.sbin/pkg: Remove unused `os_corres'.
- usr.sbin/quotaon, usr.sbin/repquota: Remove unused `qfname'.

Fix alignment related warnings reported by gcc
Switch from old style arguments to modern C
remove WARNS as a result

tested with "make universe"

Approved by: cperciva
MFC after: 1 week

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.

Cleanup of userland __P use

when no source-address-selection policy is installed, not scan
the sysctl MIB, as it leads to an unnecessary sysctl error.

Obtained from: KAME

fixed a bug that 'ip6addrctl delete' command does not work

obtained from: KAME

add ip6addrctl(8) which is a command to configure address
selection policy for IPv6 and IPv4 described in RFC3484.
source address selection part of RFC3484 is not merged
from KAME, yet.

Obtained from: KAME