Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

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

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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)

The problem is: currently our single byte ctype(3) functions are broken
for wide characters locales in the argument range >= 0x80 - they may
return false positives.

Example 1: for UTF-8 locale we currently have:
iswspace(0xA0)==1 and isspace(0xA0)==1
(because iswspace() and isspace() are the same code)
but must have
iswspace(0xA0)==1 and isspace(0xA0)==0
(because there is no such character and all others in the range
0x80..0xff for the UTF-8 locale, it keeps ASCII only in the single byte
range because our internal wchar_t representation for UTF-8 is UCS-4).

Example 2: for all wide character locales isalpha(arg) when arg > 0xFF may
return false positives (must be 0).
(because iswalpha() and isalpha() are the same code)

This change address this issue separating single byte and wide ctype
and also fix iswascii() (currently iswascii() is broken for
arguments > 0xFF).
This change is 100% binary compatible with old binaries.

Reviewied by: i18n@

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

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

. Static'ize functions exported via function reference variables only.
. Replace inclusion of sys/param.h to sys/cdefs.h and sys/types.h where
appropriate.
. move _*_init() prototypes to mblocal.h, and remove these prototypes
from .c files
. use _none_init() in __setrunelocale() instead of duplicating code
. move __mb* variables from table.c to none.c allowing us to not to
export _none_*() externs, and appropriately remove them from mblocal.h

Ok'ed by: tjr

Use a simpler and faster buffering scheme for partial multibyte characters.

Fix braino in previous: check that the second byte in the character
buffer is non-null when the character is two bytes long, not when
the buffer is two bytes long.

Move prototypes of various encoding-related functions into a new header
file to avoid extern'ing them all over the place.

In the absence of proper validation, at least check that null bytes
do not appear as anything but the first byte of a multibyte character.

Perform some basic validation of multibyte conversion state objects.

Don't cast away const qualifiers.

Spotted by: bde

Allow partial multibyte characters to accumulate in conversion state
objects passed to mbrtowc(), mbsrtowcs(), and mbrlen(), as required
by C99.

First byte of GBK-like sequences is 0x81, not 0x80

Remove unused #includes.

Implement mbrtowc() and wcrtomb() directly (sync with big5.c).

Add GBK encoding

PR: 51504
Submitted by: Statue <statue@freebsd.sinica.edu.tw>