Revert r330897:

This was intended to be a non-functional change. It wasn't. The commit
message was thus wrong. In addition it broke arm, and merged crypto
related code.

Revert with prejudice.

This revert skips files touched in r316370 since that commit was since
MFCed. This revert also skips files that require $FreeBSD$ property
changes.

Thank you to those who helped me get out of this mess including but not
limited to gonzo, kevans, rgrimes.

Requested by: gjb (re)

Partial merge of the SPDX changes

These changes are incomplete but are making it difficult
to determine what other changes can/should be merged.

No objections from: pfg

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

Implement xlocale APIs from Darwin, mainly for use by libc++. This adds a
load of _l suffixed versions of various standard library functions that use
the global locale, making them take an explicit locale parameter. Also
adds support for per-thread locales. This work was funded by the FreeBSD
Foundation.

Please test any code you have that uses the C standard locale functions!

Reviewed by: das (gdtoa changes)
Approved by: dim (mentor)

Introduce a local variable and use it instead of passed in parameter
to get rid of restrict qualifier discarding. This lets libc compile
cleanly in gnu99 mode.

Suggested by: kib, christoph.mallon at gmx.de
Approved by: kib (mentor)

Implement the GNU extensions of mbsnrtowcs() and wcsnrtombs(). These are
convenient when the source string isn't null-terminated.

Implement the other conversion functions (mbstowcs(), mbsrtowcs(), wcstombs(),
wcsrtombs()) in terms of these new functions.

Allow encoding modules to override the default implementations of
mbsrtowcs() and wcsrtombs(). Provide a fast implementation for the
trivial "NONE" encoding.

Begin in the initial shift state in mbstowcs() and wcstombs().
(This change is non-functional since nothing uses states yet.)

Prepare to handle state-dependent encodings. This mainly involves not
taking shortcuts when it comes to storing and passing around conversion
states.

Implement mbstowcs() as a wrapper around mbsrtowcs(), and wcstombs()
as a wrapper around wcsrtombs().

Style sweep.

Style: One space between "restrict" qualifier and "*".

Add restrict qualifiers to the arguments of mbstowcs, mbtowc() and
wcstombs().

Implement the XSI extension which allows the destination string to be
NULL, and returns the number of bytes that would be required to store
the result of the conversion without storing anything.

PR: 17694

Split ansi.c into a separate source file for each function.