sys: Remove $FreeBSD$: two-line .h pattern

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

sys/sys: further adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 2-Clause license, however the tool I
was using misidentified many licenses so this was mostly a manual - error
prone - task.

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.

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

Fix the visibility of several prototypes. Also move pthread_kill() and
pthread_sigmask() to signal.h. In principle, this shouldn't break anything,
since they're already in signal.h on other systems, and the FreeBSD
manpage says that both pthread.h and signal.h need to be included to
get these functions.

Add a hack to declare pthread_t in the P1003.1-2008 namespace
in signal.h.

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

According to:
http://www.opengroup.org/onlinepubs/009695399/basedefs/sys/types.h.html

#include <sys/types.h>
should include the definitions of pthread types.

PR: standards/78907
Reported by: Brooks Davis
Approved by: das (mentor)