sys: 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

sys: Remove $FreeBSD$: one-line .c comment pattern

Remove /^/[*/]\s*\$FreeBSD\$.*\n/

sys: 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.

Restore the ABI of 'struct fpreg' on powerpc.

The PT_{GET,SET}FPREGS requests use 'struct fpreg' and the NT_FPREGSET
core note stores a copy of 'struct fpreg'. As with x86 and the floating
point state there compared to the extended state in XSAVE, struct fpreg
on powerpc now only holds the 'base' FP state, and setting it via
PT_SETFPREGS leaves the extended vector state in a thread unchanged.

Reviewed by: jhibbits
Differential Revision: https://reviews.freebsd.org/D5004

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

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

Resolve warnings exposed by LINT.
o Put prototypes in a single header only.
o Fix printf format specifiers.

Add a floating-point emulator so that a single userland or single ABI
can run on processors that don't have a FPU. This is typically the
case for Book E processors. While a tuned system will probably want
to use soft-float (or use a processor that has a FPU if the usage is
FP intensive enough), allowing hard-float on FPU-less systems gives
great portability and flexibility.

Obtained from: NetBSD