Fix libxml2 2.12.x build issues.
https://github.com/php/php-src/commit/0a39890c967aa57225bb6bdf4821aff7a3a3c082
--- a/ext/libxml/libxml.c	2024-04-10 00:53:50.000000000 -0500
+++ b/ext/libxml/libxml.c	2024-05-17 07:21:47.000000000 -0500
@@ -483,7 +483,11 @@
 	xmlResetError((xmlErrorPtr) ptr);
 }
 
-static void _php_list_set_error_structure(xmlErrorPtr error, const char *msg)
+#if LIBXML_VERSION >= 21200
+static void _php_list_set_error_structure(const xmlError *error, const char *msg)
+#else
+static void _php_list_set_error_structure(xmlError *error, const char *msg)
+#endif
 {
 	xmlError error_copy;
 	int ret;
@@ -736,7 +740,11 @@
 	va_end(args);
 }
 
+#if LIBXML_VERSION >= 21200
+PHP_LIBXML_API void php_libxml_structured_error_handler(void *userData, const xmlError *error)
+#else
 PHP_LIBXML_API void php_libxml_structured_error_handler(void *userData, xmlErrorPtr error)
+#endif
 {
 	_php_list_set_error_structure(error, NULL);
 
@@ -1009,11 +1017,9 @@
 /* {{{ Retrieve last error from libxml */
 PHP_FUNCTION(libxml_get_last_error)
 {
-	xmlErrorPtr error;
-
 	ZEND_PARSE_PARAMETERS_NONE();
 
-	error = xmlGetLastError();
+	const xmlError *error = xmlGetLastError();
 
 	if (error) {
 		object_init_ex(return_value, libxmlerror_class_entry);