zoneinfo: Updated to 2024b release.

[Wedmer]

Maintainer: me
Compile tested: TI OMAP3/4/AM33xx, default, OpenWRT master
Run tested: n/a

Description:

This release contains the following changes:

Briefly:

 Improve historical data for Mexico, Mongolia, and Portugal.
 System V names are now obsolescent.
 The main data form now uses %z.
 The code now conforms to RFC 8536 for early timestamps.
 Support POSIX.1-2024, which removes asctime_r and ctime_r.
 Assume POSIX.2-1992 or later for shell scripts.
 SUPPORT_C89 now defaults to 1.

Changes to past timestamps

 Asia/Choibalsan is now an alias for Asia/Ulaanbaatar rather than
 being a separate Zone with differing behavior before April 2008.
 This seems better given our wildly conflicting information about
 Mongolia's time zone history.  (Thanks to Heitor David Pinto.)

 Historical transitions for Mexico have been updated based on
 official Mexican decrees.  The affected timestamps occur during
 the years 1921-1927, 1931, 1945, 1949-1970, and 1981-1997.
 The affected zones are America/Bahia_Banderas, America/Cancun,
 America/Chihuahua, America/Ciudad_Juarez, America/Hermosillo,
 America/Mazatlan, America/Merida, America/Mexico_City,
 America/Monterrey, America/Ojinaga, and America/Tijuana.
 (Thanks to Heitor David Pinto.)

 Historical transitions for Portugal, represented by Europe/Lisbon,
 Atlantic/Azores, and Atlantic/Madeira, have been updated based on a
 close reading of old Portuguese legislation, replacing previous data
 mainly originating from Whitman and Shanks & Pottenger.  These
 changes affect a few transitions in 1917-1921, 1924, and 1940
 throughout these regions by a few hours or days, and various
 timestamps between 1977 and 1993 depending on the region.  In
 particular, the Azores and Madeira did not observe DST from 1977 to
 1981.  Additionally, the adoption of standard zonal time in former
 Portuguese colonies have been adjusted: Africa/Maputo in 1909, and
 Asia/Dili by 22 minutes at the start of 1912.
 (Thanks to Tim Parenti.)

Changes to past tm_isdst flags

 The period from 1966-04-03 through 1966-10-02 in Portugal is now
 modeled as DST, to more closely reflect how contemporaneous changes
 in law entered into force.

Changes to data

 Names present only for compatibility with UNIX System V
 (last released in the 1990s) have been moved to 'backward'.
 These names, which for post-1970 timestamps mostly just duplicate
 data of geographical names, were confusing downstream uses.
 Names moved to 'backward' are now links to geographical names.
 This affects behavior for TZ='EET' for some pre-1981 timestamps,
 for TZ='CET' for some pre-1947 timestamps, and for TZ='WET' for
 some pre-1996 timestamps.  Also, TZ='MET' now behaves like
 TZ='CET' and so uses the abbreviation "CET" rather than "MET".
 Those needing the previous TZDB behavior, which does not match any
 real-world clocks, can find the old entries in 'backzone'.
 (Problem reported by Justin Grant.)

 The main source files' time zone abbreviations now use %z,
 supported by zic since release 2015f and used in vanguard form
 since release 2022b.  For example, America/Sao_Paulo now contains
 the zone continuation line "-3:00 Brazil %z", which is less error
 prone than the old "-3:00 Brazil -03/-02".  This does not change
 the represented data: the generated TZif files are unchanged.
 Rearguard form still avoids %z, to support obsolescent parsers.

 Asia/Almaty has been removed from zonenow.tab as it now agrees
 with Asia/Tashkent for future timestamps, due to Kazakhstan's
 2024-02-29 time zone change.  Similarly, America/Scoresbysund
 has been removed, as it now agrees with America/Nuuk due to
 its 2024-03-31 time zone change.

Changes to code

 localtime.c now always uses a TZif file's time type 0 to handle
 timestamps before the file's first transition.  Formerly,
 localtime.c sometimes inferred a different time type, in order to
 handle problematic data generated by zic 2018e or earlier.  As it
 is now safe to assume more recent versions of zic, there is no
 longer a pressing need to fail to conform RFC 8536 section 3.2,
 which requires using time type 0 in this situation.  This change
 does not affect behavior when reading TZif files generated by zic
 2018f and later.

 POSIX.1-2024 removes asctime_r and ctime_r and does not let
 libraries define them, so remove them except when needed to
 conform to earlier POSIX.  These functions are dangerous as they
 can overrun user buffers.  If you still need them, add
 -DSUPPORT_POSIX2008 to CFLAGS.

 The SUPPORT_C89 option now defaults to 1 instead of 0, fixing a
 POSIX-conformance bug introduced in 2023a.

 tzselect now supports POSIX.1-2024 proleptic TZ strings.  Also, it
 assumes POSIX.2-1992 or later, as practical porting targets now
 all support that, and it uses some features from POSIX.1-2024 if
 available.

Changes to build procedure

 'make check' no longer requires curl and Internet access.

 The build procedure now assumes POSIX.2-1992 or later, to simplify
 maintenance.  To build on Solaris 10, the only extant system still
 defaulting to pre-POSIX, prepend /usr/xpg4/bin to PATH.

Changes to documentation

 The documentation now reflects POSIX.1-2024.

Changes to commentary

 Commentary about historical transitions in Portugal and her former
 colonies has been expanded with links to many relevant legislation.
 (Thanks to Tim Parenti.)