MFC r346054: libc: update strstr implementation to match musl

musl commits:
122d67f846cb0be2c9e1c3880db9eb9545bbe38c
0239cd0681e889a269fb7691f60e81ef8d081e6b
8f5a820d147da36bcdbddd201b35d293699dacd8

MFC r346054: libc: update strstr implementation to match musl

musl commits:
122d67f846cb0be2c9e1c3880db9eb9545bbe38c
0239cd0681e889a269fb7691f60e81ef8d081e6b
8f5a820d147da36bcdbddd201b35d293699dacd8

Submitted by: David CARLIER <devnexen_gmail.com>
Obtained from: musl
MFC after: 1 week

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General 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 f

General 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.

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libc: add reference to two-way algorithm and bad shift table in memmem/strstr

Requested by: ed

libc: Use musl's O(n) memmem and strstr

It is O(n) in the length of the haystack (big) string, and has special
cases for short needle (little) strings, of one to four bytes, to avoid
excessive overh

libc: Use musl's O(n) memmem and strstr

It is O(n) in the length of the haystack (big) string, and has special
cases for short needle (little) strings, of one to four bytes, to avoid
excessive overhead.

There are a small set of nearly trivial cases where the startup overhead
of the musl implementation makes it slightly slower -- for example, a 31
byte needle that matches the beginning of the haystack. It's faster for
non-trivial cases, and significantly so for inputs that trigger worst-
case behaviour of the previous implementation. As an example, in my
tests a 16K needle that matches the end of a 64K haystack is nearly
2000x faster with this implementation.

Reviewed by: bapt (earlier), ed (earlier)
Obtained from: musl (snapshot at commit c718f9fc)
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D2601

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Renumber clauses to reduce diffs to other versions

NetBSD, OpenBSD, and Android's Bionic number the clauses 1 through 3,
so follow suit to make comparison easier.

- ANSIfy function definitions
- use nul when we are looking for a terminating character where appropriate

Approved by: imp

Per Regents of the University of Calfornia letter, remove advertising
clause.

# If I've done so improperly on a file, please let me know.

Remove 'register' keyword.

rcsid[]->__FBSDID

Make the rcsid and FreeBSD IDs more sane in the wcs* and wmem* files.
Do the same for the non-wcs*/wmem* files while I'm here.

BSD 4.4 Lite Lib Sources