Bug 1228355

Package rubygem-nokogiri fails to build with GCC 14 because of various
C99 violations which previously just generated warning s but which
cause errors with GCC 14 by default.  For more information see
https://gcc.gnu.org/gcc-14/porting_to.html and meta bug #1220571.

BuildService failures are available online at:
https://build.opensuse.org/package/live_build_log/openSUSE:Factory:Staging:Gcc7/rubygem-nokogiri/standard/x86_64

The build with GCC 14 can now be tried locally with:
osc build --clean --alternative-project home:rguenther:nextgcc

The (first) error that stops the build is:

[   17s] html4_document.c: In function ‘rb_html_document_s_read_io’:
[   17s] html4_document.c:49:52: error: passing argument 2 of ‘xmlSetStructuredErrorFunc’ from incompatible pointer type [-Wincompatible-pointer-types]
[   17s]    49 |   xmlSetStructuredErrorFunc((void *)rb_error_list, Nokogiri_error_array_pusher);
[   17s]       |                                                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~
[   17s]       |                                                    |
[   17s]       |                                                    void (*)(void *, xmlError *) {aka void (*)(void *, struct _xmlError *)}
[   17s] In file included from /usr/include/libxml/valid.h:15,
[   17s]                  from /usr/include/libxml/parser.h:19,
[   17s]                  from ./nokogiri.h:35,
[   17s]                  from html4_document.c:1:
[   17s] /usr/include/libxml/xmlerror.h:898:57: note: expected ‘xmlStructuredErrorFunc’ {aka ‘void (*)(void *, const struct _xmlError *)’} but argument is of type ‘void (*)(void *, xmlError *)’ {aka ‘void (*)(void *, struct _xmlError *)’}
[   17s]   898 |                                  xmlStructuredErrorFunc handler);
[   17s]       |                                  ~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~
[   17s] html4_document.c: In function ‘rb_html_document_s_read_memory’:
[   17s] html4_document.c:109:52: error: passing argument 2 of ‘xmlSetStructuredErrorFunc’ from incompatible pointer type [-Wincompatible-pointer-types]
[   17s]   109 |   xmlSetStructuredErrorFunc((void *)rb_error_list, Nokogiri_error_array_pusher);
[   17s]       |                                                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~
[   17s]       |                                                    |
[   17s]       |                                                    void (*)(void *, xmlError *) {aka void (*)(void *, struct _xmlError *)}
[   17s] /usr/include/libxml/xmlerror.h:898:57: note: expected ‘xmlStructuredErrorFunc’ {aka ‘void (*)(void *, const struct _xmlError *)’} but argument is of type ‘void (*)(void *, xmlError *)’ {aka ‘void (*)(void *, struct _xmlError *)’}
[   17s]   898 |                                  xmlStructuredErrorFunc handler);
[   17s]       |                                  ~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~