Log Message:
Update to 1.4.21. From the changelog:

glass backend:

* Avoid throwing InvalidArgument when searching for overlong terms in some
  cases.  Such terms can't match, but are valid to query for.  Patch from
  Robert Stepanek in https://github.com/xapian/xapian/pull/313.

chert backend:

* Avoid throwing InvalidArgument when searching for overlong terms in some
  cases.  Such terms can't match, but are valid to query for.

build system:

* Clean up cygwin and mingw configure checks.  When we check $host_os, always
  anchor at the start (e.g. cygwin* not *cygwin*), and check for msys* as well
  since that's a derivative of cygwin and behaves similarly for the things
  we're checking here.

* Update to use AX_CXX_COMPILE_STDCXX which is a replacement for
  AX_CXX_COMPILE_STDCXX_11 (which we were using) which also supports newer C++
  standards versions which will be useful.  For C++11 the only difference seems
  to be that the macro now checks for attribute support - we use C++11
  attributes so that seems a good thing.

documentation:

* INSTALL: Restructure MSVC section for clarity.

* INSTALL: Mention -D_FORTIFY_SOURCE=3 too (fairly new - requires GCC 12).

* Consistently say "macOS" not "Mac OS X", "OS X", etc.

* admin_notes.rst:

  + Update locking section to cover Open File Description locks

  + Add some discussion of block sizes (fixes #819, reported by mgautier)

  + Fix cut-and-paste error - we were suggesting that the docdata table only
    exists if there's positional data.  Noted by Gaurav Arora.

  + Improve markup

examples:

* Stop using std::endl in examples since this seems to be C++ best practice
  as it causes a flush of the stream, which is rarely actually wanted.  Also
  often the replacement \n can be combined with a string literal.

portability:

* Stop trying to check for incompatible C++ ABI between the compiler used to
  build xapian-core and the compiler used to build code using xapian-core.

  This check was helpful in the GCC 3 days, but ABI versions 2 and up are
  compatible aside from obscure corner cases, and GCC now defaults to using the
  latest ABI version it supports.  The result is that this check is no longer
  useful enough to justify the noise.

  We still check for incompatible _GLIBCXX_DEBUG between the library and
  application builds, since that will cause things not to work, and the normal
  error message doesn't make it clear what's wrong.

  Reported by David Bremner.

* Fix new warnings from GCC 12.

* Avoid undefined value use when unpacking a key in a corrupted glass docdata
  table.  We now skip further checks on the entry in this case.

* Merge allocations in MSVC directory reading compatibility code so we can
  allocate in a single malloc() call.

* Add accept() wrapper which checks an assumption that Microsoft's SOCKET type
  only actually holds 32 bit values even in 64 bit platforms and throws an
  exception if violated.

* Eliminate a use of sprintf.

* Squash some unhelpful MSVC deprecation warnings.

* Declare dummy invalid parameter handler noexcept to fix a warning from MSVC.

* Include <stdlib.h> in configure check for sys_errlist as that's where it is
  with mingw and MSVC.

debug code:

* Fix debug logging for Xapian::Internal::intrusive_ptr<const T>.

  GCC 12.2 warned about infinite recursion in the old version, and this seems
  to be the case.  This code has been there a long time, but is only used when
  debug logging is enabled.  It does seem to be used, so presumably nobody's
  tried to log something which triggered it.

Updating during the freeze for the bug and portability fixes.