MFC r335404: sort(1): Fix -m when only implicit stdin is used for input

Observe:

printf "a\nb\nc\n" > /tmp/foo
# Next command results in no output
cat /tmp/foo | sort -m
# Next command results in proper output
cat /tmp/foo | sort -m -
# Also works:
sort -m /tmp/foo

Some const'ification was done to simplify the actual solution of adding "-"
explicitly to the file list if we didn't have any file arguments left over.

PR: 190099

MFC r326276:

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.

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Remove custom getdelim(3) and fix a small memory leak.

Originally from Andre Smagin.

Obtained from: OpenBSD
MFC after: 1 week

sort: Cleanup small issues with spaces.

Obtained from: OpenBSD

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>

- Change --nthreads parameter to --parallel for GNU compatibility
- Change default sort method to mergesort, which has a better worst case
performance than qsort

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

- Only use multi-threading for large files
- Do not use mmap() by default; it can be enabled by --mmap
- Add some minor optimizations for -u
- Update manual page according to the changes

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.