expat: update to 2.4.1

Release 2.4.1 Sun May 23 2021
        Bug fixes:
      #488 #490  Autotools: Fix installed header expat_config.h for multilib
                    systems; regression introduced in 2.4.0 by pull request #486

        Other changes:
      #491 #492  Version info bumped from 9:0:8 to 9:1:8;
                    see https://verbump.de/ for what these numbers do

        Special thanks to:
            Gentoo's QA check "multilib_check_headers"

Release 2.4.0 Sun May 23 2021
        Security fixes:
  #34 #466 #484  CVE-2013-0340/CWE-776 -- Protect against billion laughs attacks
                    (denial-of-service; flavors targeting CPU time or RAM or both,
                    leveraging general entities or parameter entities or both)
                    by tracking and limiting the input amplification factor
                    (<amplification> := (<direct> + <indirect>) / <direct>).
                    By conservative default, amplification up to a factor of 100.0
                    is tolerated and rejection only starts after 8 MiB of output bytes
                    (=<direct> + <indirect>) have been processed.
                    The fix adds the following to the API:
                    - A new error code XML_ERROR_AMPLIFICATION_LIMIT_BREACH to
                      signals this specific condition.
                    - Two new API functions ..
                      - XML_SetBillionLaughsAttackProtectionMaximumAmplification and
                      - XML_SetBillionLaughsAttackProtectionActivationThreshold
                      .. to further tighten billion laughs protection parameters
                      when desired.  Please see file "doc/reference.html" for details.
                      If you ever need to increase the defaults for non-attack XML
                      payload, please file a bug report with libexpat.
                    - Two new XML_FEATURE_* constants ..
                      - that can be queried using the XML_GetFeatureList function, and
                      - that are shown in "xmlwf -v" output.
                    - Two new environment variable switches ..
                      - EXPAT_ACCOUNTING_DEBUG=(0|1|2|3) and
                      - EXPAT_ENTITY_DEBUG=(0|1)
                      .. for runtime debugging of accounting and entity processing.
                      Specific behavior of these values may change in the future.
                    - Two new command line arguments "-a FACTOR" and "-b BYTES"
                      for xmlwf to further tighten billion laughs protection
                      parameters when desired.
                      If you ever need to increase the defaults for non-attack XML
                      payload, please file a bug report with libexpat.

        Bug fixes:
      #332 #470  For (non-default) compilation with -DEXPAT_MIN_SIZE=ON (CMake)
                    or CPPFLAGS=-DXML_MIN_SIZE (GNU Autotools): Fix segfault
                    for UTF-16 payloads containing CDATA sections.
      #485 #486  Autotools: Fix generated CMake files for non-64bit and
                    non-Linux platforms (e.g. macOS and MinGW in particular)
                    that were introduced with release 2.3.0

        Other changes:
      #468 #469  xmlwf: Improve help output and the xmlwf man page
            #463  xmlwf: Improve maintainability through some refactoring
            #477  xmlwf: Fix man page DocBook validity
      #458 #459  CMake: Support absolute paths for both CMAKE_INSTALL_LIBDIR
                    and CMAKE_INSTALL_INCLUDEDIR
      #471 #481  CMake: Add support for standard variable BUILD_SHARED_LIBS
            #457  Unexpose symbol _INTERNAL_trim_to_complete_utf8_characters
            #467  Resolve macro HAVE_EXPAT_CONFIG_H
            #472  Delete unused legacy helper file "conftools/PrintPath"
      #473 #483  Improve attribution
  #464 #465 #477  doc/reference.html: Fix XHTML validity
      #475 #478  doc/reference.html: Replace the 90s look by OK.css
            #479  Version info bumped from 8:0:7 to 9:0:8
                    due to addition of new symbols and error codes;
                    see https://verbump.de/ for what these numbers do

        Infrastructure:
            #456  CI: Enable periodic runs
            #457  CI: Start covering the list of exported symbols
            #474  CI: Isolate coverage task
      #476 #482  CI: Adapt to breaking changes in image "ubuntu-18.04"
            #477  CI: Cover well-formedness and DocBook/XHTML validity
                    of doc/reference.html and doc/xmlwf.xml

        Special thanks to:
            Dimitry Andric
            Eero Helenius
            Nick Wellnhofer
            Rhodri James
            Tomas Korbar
            Yury Gribov
                and
            Clang LeakSan
            JetBrains
            OSS-Fuzz

(nia)