Log Message:
autoconf: update to 2.72.

* Noteworthy changes in release 2.72 (2023-12-22) [release]

** Backward incompatibilities

*** Configure scripts no longer support pre-1989 C compilers.
  Specifically, compilers that *only* implement the original “K&R”
  function definition syntax, and not the newer “prototyped” syntax,
  will not be able to parse the test programs now emitted by
  AC_CHECK_FUNC, AC_LANG_CALL, and similar macros.  AC_PROG_CC still
  accepts such compilers, but this may change in the near future.

  This change was necessary in order to support the upcoming 2024
  edition of the C standard (often referred to as “C23”), which will
  officially remove the function declaration syntax used by
  AC_CHECK_FUNC in Autoconf 2.71 and earlier.  We feel that support
  for compilers that support only C 2024 is more useful, nowadays,
  than support for compilers that don’t implement a core feature of
  C 1989.

*** Autoconf developers now need Perl 5.10 (2007) or later.
  “Autoconf developers” means specifically people hacking on Autoconf
  itself.  Autoconf *users*, i.e. authors of configure.ac files and
  add-on M4 macros, still need only Perl 5.6 (2000) or later.

  We do recommend all Autoconf users upgrade to Perl 5.10 or later if
  possible, as this version significantly improves Perl’s ability to
  handle files with last-modification timestamps separated by less
  than a second.  (Note: even in the most recent release, Perl cannot
  always match the file system’s timestamp resolution.)

  Generated configure scripts continue to run without Perl.

*** Autoconf users now need GNU M4 1.4.8 (2006) or later.
  Use of GNU M4 1.4.16 or later is recommended, as all earlier versions
  are known to have had serious bugs in the text-processing builtins
  on some, but not all, operating systems.  Autoconf’s own configure
  script will attempt to find a version of M4 that is not affected by
  these bugs.

  Note: Autoconf 2.70 and 2.71 include code that malfunctions with
  M4 1.4.6 or 1.4.7.  However, the only effect of the malfunction is
  that you will get a confusing error message if you run autoconf on
  a configure.ac that neglects to use AC_INIT or AC_OUTPUT.

  Generated 'configure' scripts continue to run without M4.

*** Some m4sh diversions have been renumbered.
  This will only affect macros that use m4_divert with numbered rather
  than named diversions, which has always been strongly discouraged
  both by the documentation and with warnings.

*** AC_FUNC_GETGROUPS and AC_TYPE_GETGROUPS no longer run test programs.
  These macros were testing for OS bugs that we believe are at least
  twenty years in the past.  Most operating systems are now trusted to
  provide an accurate prototype for getgroups in unistd.h, and to
  implement it as specified in POSIX.

  AC_FUNC_GETGROUPS still includes a short block-list of OSes with
  known, severe bugs in getgroups.  It can be overridden using
  config.site.  If you encounter a mistake in this list,
  please report it to bug-autoconf.

*** All internal uses of AC_EGREP_CPP and AC_EGREP_HEADER have been removed.
  These macros look for text matching a regular expression in the
  output of the C preprocessor.  Their use has been discouraged for
  many years, as they tend to be unreliable; it is better to find a
  way to use AC_COMPILE_IFELSE or AC_PREPROC_IFELSE instead.  We have
  finally taken our own advice.

  This change might break configure scripts that expected probes for
  ‘grep’ and/or the C preprocessor to happen as a side effect of an
  unrelated operation.  Such scripts can be fixed by adding
  AC_PROG_EGREP and/or AC_PROG_CPP in an appropriate place.

  The macros affected by this change are AC_C_STRINGIZE,
  AC_C_VARARRAYS, AC_FUNC_GETGROUPS, AC_FUNC_GETLOADAVG,
  AC_HEADER_TIOCGWINSZ, AC_PROG_GCC_TRADITIONAL, AC_TYPE_GETGROUPS,
  AC_TYPE_UID_T, and AC_XENIX_DIR. Many of these macros are themselves
  obsolete; if your configure script uses any of them, check whether
  it is actually needed.

** New features

*** Support for ensuring time_t is Y2038-safe
  configure can now ensure that time_t can represent moments in time
  after 18 January 2038, i.e. 2**31 - 1 seconds after the Unix epoch.
  On most “64-bit” systems this is true by default; the new feature
  is detection of systems where time_t is a 32-bit signed integer by
  default, *and* there is an alternative mode in which it is larger,
  in which case that mode will be enabled.

  In this release, all configure scripts that use AC_SYS_LARGEFILE
  gain a new command line option --enable-year2038.  When this option
  is used, the configure script will check for and enable support for
  a large time_t.

  This release also adds two new macros, AC_SYS_YEAR2038 and
  AC_SYS_YEAR2038_RECOMMENDED.  Both have all the effects of
  AC_SYS_LARGEFILE.  (This is because it is not possible to enlarge
  time_t without also enlarging off_t, on any system we are aware of.)

  AC_SYS_YEAR2038 additionally flips the default for --enable-year2038;
  a configure script that uses this macro will check for and enable
  support for a large time_t by default, but this can be turned off by
  using --disable-year2038.  AC_SYS_YEAR2038_RECOMMENDED goes even
  further, and makes the configure script fail on systems that do not
  seem to support timestamps after 18 January 2038 at all.  This
  failure can be suppressed by using --disable-year2038.

  Changing the size of time_t can change a library’s ABI.  Therefore,
  application and library builders should take care that all packages
  are configured with consistent use of --enable-year2038 or
  --disable-year2038, to ensure binary compatibility.  This is similar
  to longstanding consistency requirements with --enable-largefile and
  --disable-largefile.

  In this release, these macros only know how to enlarge time_t on two
  classes of systems: 32-bit MinGW, and any system where time_t can be
  enlarged by defining the preprocessor macro _TIME_BITS with the
  value 64.  At the time this NEWS entry was written, only GNU libc
  (version 2.34 and later) supported the latter macro.  Authors of
  other C libraries with a 32-bit time_t are encouraged to adopt
  _TIME_BITS, rather than inventing a different way to enlarge time_t.

*** AC_USE_SYSTEM_EXTENSIONS now enables C23 Annex F extensions
  by defining __STDC_WANT_IEC_60559_EXT__.

** Obsolete features and new warnings

*** Autoconf now quotes 'like this' instead of `like this'.
  Autoconf’s diagnostics now follow current GNU coding standards,
  which say that diagnostics in the C locale should quote 'like this'
  with plain apostrophes instead of the older GNU style `like this'
  with grave accent and apostrophe.

*** AC_PROG_GCC_TRADITIONAL no longer does anything.
  This macro has had no useful effect since GCC dropped support for
  traditional-mode compilation in version 3.3 (released in 2003), and
  the systems that needed it are also long obsolete.  It is now a
  compatibility synonym for AC_PROG_CC.

** Notable bug fixes

*** autom4te now uses fine-grained file timestamps
  Autoconf’s internal “autom4te” utility is now able to compare file
  modification timestamps with sub-second precision, when available.
  This eliminates a class of bugs where autom4te fails to regenerate
  an outdated file.  Automake 1.17 (forthcoming) is required for a
  complete fix.

*** AC_HEADER_STDBOOL, AC_CHECK_HEADER_STDBOOL are obsolescent and less picky.
  These macros are now obsolescent, as most programs can simply include
  stdbool.h unconditionally.  If you use these macros, they now accept
  a stdbool.h that exists but does nothing, so long as ‘bool’, ‘true’,
  and ‘false’ work anyway.  This is for compatibility with C23 and
  with C++.

*** AC_PROG_MKDIR_P now falls back on plain 'mkdir -p'.
  When AC_PROG_MKDIR_P cannot find a mkdir implementation that is
  known to lack race condition bugs, it now falls back on 'mkdir -p'
  instead of falling back on a relative path to install-sh, as the
  relative paths now seem to be a more important problem than the
  problems of ancient mkdir implementations with race condition bugs.
  See <https://savannah.gnu.org/support/?110740>.  The only ancient
  mkdir still supported is Solaris 10 /usr/bin/mkdir, and for that
  platform AC_PROG_MKDIR_P falls back on /opt/sfw/bin/mkdir which
  should work if it is installed; if not, you should avoid parallel
  'make' on that platform.

*** Better diagnostics for calling m4_warn() with a bad first argument
  Calling m4_warn with a first argument that doesn’t match any of the
  official warning categories now produces a sensible error message,
  instead of something that makes it look like there’s a bug in the
  guts of autom4te.  Also, the documentation has been adjusted in
  several places to make it clearer what the official warning
  categories are.

  Note: In Autoconf 2.69 and earlier, the manual said that [] and [all]
  could be used as the first argument to m4_warn.  This was incorrect,
  even at the time.

*** Improved compatibility with a wide variety of systems and tools
  including CheriBSD, Darwin (macOS), GNU Guix, OS/2, z/OS, Bash 5.2,
  the BusyBox shell and utilities, Clang/LLVM version 16, the upcoming
  GCC version 14, etc.

** Known bugs

*** AC_SYS_LARGEFILE and AC_SYS_YEAR2038 only work correctly in C mode.

  This is only a problem for configure scripts that invoke either
  macro while AC_LANG([something other than C]) is in effect, and
  will only be a *visible* problem on systems where support
  for large files and/or timestamps after 2038 are *available*
  but not enabled by default.

  This is the cause of the AC_SYS_LARGEFILE, AC_SYS_YEAR2038, and/or
  AC_SYS_YEAR2038_RECOMMENDED testsuite failures on some systems.
  See <https://savannah.gnu.org/support/index.php?110983> for details
  and a workaround.