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

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spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix

sort(1): Memoize MD5 computation to reduce repeated computation

Experimentally, reduces sort -R time of a 148160 line corpus from about
3.15s to about 0.93s on this particular system.

There's probably room for improvement using some digest other than md5, but
I don't want to look at sort(1) anymore. Some discussion of other possible
improvements in the Test Plan section of the Differential.

PR: 230792
Reviewed by: jhb (earlier version)
Differential Revision: https://reviews.freebsd.org/D19885

various: general 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.

No functional change intended.

- Use correct offsets into the keys set array. As the elements of this
zero-length array are dynamically sized at run-time based on the use
of hints, compilers can't be expected to figure out these offsets on
their own. [1]
- Fix incorrect comparison in cmp_nans(). [2]

PR: 204571 [1], 202301 [2]
Submitted by: David Binderman [2]
MFC after: 3 days

Various style(9) fixes and typos in grep, sort and patch.

MFC after: 3 days

- Update Oleg Moskalenko's email address

Requested by: Oleg Moskalenko <mom040267@gmail.com>

- Portability changes for ARM
- Allow larger sort memory on 64-bit platforms

Submitted by: Oleg Moskalenko <oleg.moskalenko@citrix.com>

Add a BSD-licensed sort rewrite that was started by me and later completed
with the major functionality and optimizations by Oleg Moskalenko.
It is compatible with the latest version of POSIX and the current GNU sort
version that we have in base. Beside this, it implements all the
functionality introduced in later versions of GNU sort. For now, it will
be installed as "bsdsort", keeping GNU sort as the default sort
implementation.