[php-src] Issue #13517: Multiple test failures when building with --with-expat

Issue: https://github.com/php/php-src/issues/13517 Author: hannob ### Description Compiling latest php with expat support (./configure --with-expat; make; make test) leads to multiple test failures in xml-related tests. I'll attach the test output. I'm unsure about the support status of expat in php. This doc https://www.php.net/manual/en/xml.requirements.php implies that with that option, it would use expat as its xml backend. But when building, it links against both libxml2 and expat, and I'm unsure what the implications are. Those docs also link to a very old expat webpage, and the notes about building expat are probably obsolete. I think it would be good to update and clarify those docs. This is I believe the relevant part from the test log: ``` FAILED TEST SUMMARY --------------------------------------------------------------------- ReflectionExtension::getDependencies() [ext/reflection/tests/016.phpt] Test setlocale() function : usage variations - setting system locale = 0 [ext/standard/tests/strings/setlocale_variation3.phpt] Test setlocale() function : usage variations - setting system locale as null [ext/standard/tests/strings/setlocale_variation4.phpt] Test setlocale() function : usage variations - Setting system locale as empty string [ext/standard/tests/strings/setlocale_variation5.phpt] Bug #26614 (CDATA sections skipped on line count) [ext/xml/tests/bug26614_libxml_gte2_11.phpt] Bug #46699: (xml_parse crash when parser is namespace aware) [ext/xml/tests/bug46699.phpt] Bug #81351 (xml_parse may fail, but has no error code) [ext/xml/tests/bug81351.phpt] xml_error_string() - Basic test on 5 error codes [ext/xml/tests/xml_error_string_basic.phpt] Test xml_set_start_namespace_decl_handler function: basic [ext/xml/tests/xml_set_start_namespace_decl_handler_basic.phpt] ``` (The setlocale failures seem unrelated to expat/xml, they also appear when building with default options) [php_test_results_20240226_1616.txt](https://github.com/php/php-src/files/14407381/php_test_results_20240226_1616.txt) ### PHP Version PHP 8.3.3 ### Operating System _No response_