Remove $FreeBSD$: one-line .c pattern

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

spdx: The BSD-2-Clause-NetBSD identifier is obsolete, drop -NetBSD

The SPDX folks have obsoleted the BSD-2-Clause-NetBSD 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

gzip: fix error handling in unxz

The result of fstat() was not checked. Furthermore, there was a
redundant check of st.st_size. Fix both.

Reported by: Coverity
MFC after: 1 week
Sponsored by: Dell EMC Isilon

Port NetBSD improvements:

- Add -l support for xz files
- Add lzip support to gzip based on the example lzip decoder.

Obtained from: NetBSD
MFC after: 2 weeks
Relnotes: yes

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.

Support SIGINFO.

Obtained from: NetBSD
MFC after: 2 weeks

Reflect actual NetBSD revision we already have.

MFC after: 3 days

According to the NetBSD foundation [1]:

Third parties are encouraged to change the license on any files which have
a 4-clause license contributed to the NetBSD Foundation to a 2-clause
license. We would also encourage you to inform us about these files, so
that we can continue to track the many places in which NetBSD is used.

http://www.netbsd.org/about/redistribution.html#why2clause [1]

Requested by: joel@

Incorporate recent changes from NetBSD. Most notable change is the addition
of support of decompressing xz files.

Obtained from: NetBSD