Build fails with libxml2 2.14.2

[marcriera]

On Arch Linux, with the latest libxml2 (2.14.2), build fails due to changes in the library:

[ 67%] Building CXX object lttoolbox/CMakeFiles/lt-comp.dir/lt_comp.cc.o
In file included from /usr/include/libxml2/libxml/encoding.h:26,
                 from /home/marc/apertium/Development/lttoolbox/lttoolbox/xml_parse_util.h:20,
                 from /home/marc/apertium/Development/lttoolbox/lttoolbox/entry_token.h:23,
                 from /home/marc/apertium/Development/lttoolbox/lttoolbox/compiler.h:21,
                 from /home/marc/apertium/Development/lttoolbox/lttoolbox/lt_comp.cc:17:
/home/marc/apertium/Development/lttoolbox/lttoolbox/lt_comp.cc: In function ‘int main(int, char**)’:
/usr/include/libxml2/libxml/xmlerror.h:22:69: error: invalid type argument of unary ‘*’ (have ‘long int’)
   22 | #define initGenericErrorDefaultFunc(h) xmlSetGenericErrorFunc(NULL, *(h))
      |                                                                     ^~~~
/home/marc/apertium/Development/lttoolbox/lttoolbox/lt_comp.cc:122:3: note: in expansion of macro ‘initGenericErrorDefaultFunc’
  122 |   initGenericErrorDefaultFunc(NULL);
      |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~
make[2]: *** [lttoolbox/CMakeFiles/lt-comp.dir/build.make:79: lttoolbox/CMakeFiles/lt-comp.dir/lt_comp.cc.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:314: lttoolbox/CMakeFiles/lt-comp.dir/all] Error 2
make: *** [Makefile:146: all] Error 2