Sync with upstream tzcode (2015g).

Sync with upstream tzcode (2015g).

This is quite a large patch because we haven't updated for some time,
but the good news is that upstream is now thread-safe so a lot of our
changes go away in this update and the remaining diff is a lot smaller.

(Note that our whitespace still doesn't match upstream. I use diff -wub
to compare. Upstream doesn't even really have a consistent style. New
code seems to be two spaces, old code tabs.)

From the intervening changelogs (eliding the changes that only affected
the tools, which we don't use):

2014a:
     An uninitialized-storage bug in 'localtime' has been fixed.
     (Thanks to Logan Chien.)

2014b:
     'zic' and 'localtime' no longer reject locations needing four
     transitions per year for the forseeable future.  (Thanks to Andrew
     Main (Zefram).)

2014c:
     <None>

2014d:
     <None>

2014e:
     <None>

2014f:
     'localtime', 'mktime', etc. now use much less stack space if
     ALL_STATE is defined.  (Thanks to Elliott Hughes for reporting the
     problem.)

     Some lint has been removed when using GCC_DEBUG_FLAGS with GCC
     4.9.0.

2014g:
     Unless NETBSD_INSPIRED is defined to 0, the tz library now
     supplies functions for creating and using objects that represent
     time zones. The new functions are tzalloc, tzfree, localtime_rz,
     mktime_z, and (if STD_INSPIRED is also defined) posix2time_z and
     time2posix_z.  They are intended for performance: for example,
     localtime_rz (unlike localtime_r) is trivially thread-safe without
     locking.  (Thanks to Christos Zoulas for proposing NetBSD-inspired
     functions, and to Alan Barrett and Jonathan Lennox for helping to
     debug the change.)

     If THREAD_SAFE is defined to 1, the tz library is now thread-safe.
     Although not needed for tz's own applications, which are single-threaded,
     this supports POSIX better if the tz library is used in multithreaded apps.

     Some crashes have been fixed when zdump or the tz library is given
     invalid or outlandish input.

     The tz library no longer mishandles leap seconds on platforms with
     unsigned time_t in time zones that lack ordinary transitions after 1970.

     The tz code now attempts to infer TM_GMTOFF and TM_ZONE if not
     already defined, to make it easier to configure on common platforms.
     Define NO_TM_GMTOFF and NO_TM_ZONE to suppress this.

     Unless the new macro UNINIT_TRAP is defined to 1, the tz code now
     assumes that reading uninitialized memory yields garbage values
     but does not cause other problems such as traps.

     If TM_GMTOFF is defined and UNINIT_TRAP is 0, mktime is now
     more likely to guess right for ambiguous time stamps near
     transitions where tm_isdst does not change.

     If HAVE_STRFTIME_L is defined to 1, the tz library now defines
     strftime_l for compatibility with recent versions of POSIX.
     Only the C locale is supported, though.  HAVE_STRFTIME_L defaults
     to 1 on recent POSIX versions, and to 0 otherwise.

     tzselect -c now uses a hybrid distance measure that works better
     in Africa.  (Thanks to Alan Barrett for noting the problem.)

     The C source code now ports to NetBSD when GCC_DEBUG_FLAGS is used,
     or when time_tz is defined.

     When HAVE_UTMPX_H is set the 'date' command now builds on systems
     whose <utmpx.h> file does not define WTMPX_FILE, and when setting
     the date it updates the wtmpx file if _PATH_WTMPX is defined.
     This affects GNU/Linux and similar systems.

     For easier maintenance later, some C code has been simplified,
     some lint has been removed, and the code has been tweaked so that
     plain 'make' is more likely to work.

     The C type 'bool' is now used for boolean values, instead of 'int'.

     The long-obsolete LOCALE_HOME code has been removed.

     The long-obsolete 'gtime' function has been removed.

2014h:
     The tz library's localtime and mktime functions now set tzname to a value
     appropriate for the requested time stamp, and zdump now uses this
     on platforms not defining TM_ZONE, fixing a 2014g regression.
     (Thanks to Tim Parenti for reporting the problem.)

     The tz library no longer sets tzname if localtime or mktime fails.

     An access to uninitalized data has been fixed.
     (Thanks to Jörg Richter for reporting the problem.)

     When THREAD_SAFE is defined, the code ports to the C11 memory model.
     A memory leak has been fixed if ALL_STATE and THREAD_SAFE are defined
     and two threads race to initialize data used by gmtime-like functions.
     (Thanks to Andy Heninger for reporting the problems.)

2014i:
     The time-related library functions now set errno on failure,
     and some crashes in the new tzalloc-related library functions
     have been fixed.  (Thanks to Christos Zoulas for reporting
     most of these problems and for suggesting fixes.)

     If USG_COMPAT is defined and the requested time stamp is
     standard time, the tz library's localtime and mktime functions
     now set the extern variable timezone to a value appropriate
     for that time stamp; and similarly for ALTZONE, daylight
     saving time, and the altzone variable.  This change is a
     companion to the tzname change in 2014h, and is designed to
     make timezone and altzone more compatible with tzname.

     The tz library's functions now set errno to EOVERFLOW if they
     fail because the result cannot be represented.  ctime and
     ctime_r now return NULL and set errno when a time stamp is out
     of range, rather than having undefined behavior.

     Some bugs associated with the new 2014g functions have been
     fixed.  This includes a bug that largely incapacitated the new
     functions time2posix_z and posix2time_z.  (Thanks to Christos
     Zoulas.)  It also includes some uses of uninitialized
     variables after tzalloc.  The new code uses the standard type
     'ssize_t', which the Makefile now gives porting advice about.

2014j:
     <None>

2015a:
     tzalloc now scrubs time zone abbreviations compatibly with the way
     that tzset always has, by replacing invalid bytes with '_' and by
     shortening too-long abbreviations.

2015b:
     Fix integer overflow bug in reference 'mktime' implementation.
     (Problem reported by Jörg Richter.)

     Allow -Dtime_tz=time_t compilations, and allow -Dtime_tz=... libraries
     to be used in the same executable as standard-library time_t functions.
     (Problems reported by Bradley White.)

2015c:
     <None>

2015d:
     <None>

2015e:
     <None>

2015f:
     <None>

2015g:
    localtime no longer mishandles America/Anchorage after 2037.
    (Thanks to Bradley White for reporting the bug.)

    On hosts with signed 32-bit time_t, localtime no longer mishandles
    Pacific/Fiji after 2038-01-16 14:00 UTC.

    The localtime module allows the variables 'timezone', 'daylight',
    and 'altzone' to be in common storage shared with other modules,
    and declares them in case the system <time.h> does not.
    (Problems reported by Kees Dekker.)

    On platforms with tm_zone, strftime.c now assumes it is not NULL.
    This simplifies the code and is consistent with zdump.c.
    (Problem reported by Christos Zoulas.)

Change-Id: I9eb0a8323cb8bd9968fcfe612dc14f45aa3b59d2