libc/locale: Nix needless size_t casts.

No functional change intended. No binary change to aarch64 libc.

Prompted by code inspection around PR lib/58319.

Don't overalign _RuneStatePriv, it must share the alignment of mbstate_t
it aliased with. Assert that the alignment actually used reflects the
alignment required by existing implementation and for newly build
modules assert that it is at most the guaranteed alignment.

branches: 1.6.20;
Rename fixup to update_global to better reflect the purpose.
Remove the various Current pointers, they are implementation internals
that shouldn't be leaked. Remove _CATEGORY_DEFAULT related handling and
directly pick the implemenation pointer from the C locale.
Merge the C locale data into global_locale.c with the exception of
_DefaultRuneLocale. Mark that one hidden. Move _RUNE_LOCALE and
_CITRUS_CTYPE into multibyte.h and pick up the correct rl_citrus_ctype
for non-default locales.

branches: 1.5.8; 1.5.14;
merge christos-time_t

Fixes PR lib/39662, shortcomings in LC_{MONETARY,NUMERIC,TIME,MESSAGES} db format.
ok'ed by core and releng.
(thanks for agc@, snj@ and i'm sorry for long time patience).

[libc]
- localeio.[ch] and lc*.[ch] in src/lib/libc/locale was replaced by
new locale-db implementation using citrus_db backend,
see src/lib/libc/citrus/citrus_lc_*.[ch].
- add citrus_bcs_strtou?l.c. don't use strtou?l locale implementation
internally, because they're locale-aware function.
- add some stubs for multi-locale issue, see {current,global}_locale.c.
- remove some obsolete file, setrunelocale.c, ___runetype_mb.c.
- remove __savectype() from ctypeio.[ch].

[tools]
- mklocale(1): add new option ``-t'' that generates new style
LC_{MONETARY,NUMERIC,TIME,MESSAGES} locale-db format.
- chrtbl(1): added ctypeio.[ch] for __savectype().

[locale-db]
- added en_US.US-ASCII locale.
- removed some shareable locale definition file:
en_US.US-ASCII -> en_US.ISO8859-1, en_US.UTF-8
zh_CN.eucCN -> zh_CN.GB18030
and more...see src/share/locale/*/Makefile.
- remove obsoleted locale sr_YU, added new locale sr_ME, sr_RS.
- change locale name ja_JP.ISO2022-JP* -> ja_JP.ISO-2022-JP*
for X11's locale.alias file alignments.
- fix regression test, wrong wcs?width(3), NAN/INF usage.

i tested release-build following arch:
i386, amd64, hpc{mips,arm,sh}, sparc64, vax.

citrus_lc_*.[ch] also can read old-plain-text style locale-db.
so that backward compatibility is keeped, but lc*.[ch] can't read
new citrus_db'ed locale-db and localeio.c never check sanity,
so forward compatibility is broken ;-<

old mklocale(1) doesn't know -t option, so you have to rebuild toolchain.

branches: 1.3.38; 1.3.40;
The fourth parameter of _citrus_ctype_mbrtowc() is a size_t, not a
pointer type. So use 0 instead of NULL.

branches: 1.2.2;
Move mbstate_t materials from locale/runetype.h to locale/multibyte.h.
Before this fix, building nbmklocale was failed on non-NetBSD-current platforms.
multibyte.h seems more appropriate one to contain them.

refine i18n stuffs.
- add libc/citrus directory.
this directory contains the common stuffs not only for locale
but also other facilities relating to i18n (e.g. iconv).
- To keep the binary compatibility for the ctype modules easily,
the interface between libc and the modules is simplified.
- For the future integrated extension, module pool is renamed
from "/usr/lib/runemodule" to "/usr/lib/i18n".
In the future, this directory will contain the modules for "iconv",
"collation", etc.
- some cosmetic changes.
- Bug fix for runetype.h; __attribute__((__packed__)) is placed at
the wrong position and it is invalid unintentionally.
But, the all members of the structures seem well-aligned. Thus,
this bug causes no problem, hopefully.

HEADS UP:
- /usr/lib/rumemodule is obsoleted. If you use the multibyte locales,
you need to install /usr/lib/i18n/* from sys/lib/i18n_module .
- The binary compatibility of /usr/share/locale/*/LC_CTYPE is probably kept.
Perhaps, the bug fix about __packed__ mentioned above breaks the
compatibility... Be careful especially on 64bit platforms.