Fixes the following error

/home/builder/.termux-build/postgresql/src/src/backend/utils/adt/xml.c:1177:45: error: incompatible function pointer types passing 'void (void *, xmlErrorPtr)' (aka 'void (void *, struct _xmlError *)') to parameter of type 'xmlStructuredErrorFunc' (aka 'void (*)(void *, const struct _xmlError *)') [-Wincompatible-function-pointer-types]
        xmlSetStructuredErrorFunc((void *) errcxt, xml_errorHandler);
                                                   ^~~~~~~~~~~~~~~~
/data/data/com.termux/files/usr/include/libxml2/libxml/xmlerror.h:898:29: note: passing argument to parameter 'handler' here
                                 xmlStructuredErrorFunc handler);
                                                        ^

--- a/src/backend/utils/adt/xml.c
+++ b/src/backend/utils/adt/xml.c
@@ -123,7 +123,7 @@
 										   xmlParserCtxtPtr ctxt);
 static void xml_errsave(Node *escontext, PgXmlErrorContext *errcxt,
 						int sqlcode, const char *msg);
-static void xml_errorHandler(void *data, xmlErrorPtr error);
+static void xml_errorHandler(void *data, const struct _xmlError *error);
 static int	errdetail_for_xml_code(int code);
 static void chopStringInfoNewlines(StringInfo str);
 static void appendStringInfoLineSeparator(StringInfo str);
@@ -2002,7 +2002,7 @@
  * Error handler for libxml errors and warnings
  */
 static void
-xml_errorHandler(void *data, xmlErrorPtr error)
+xml_errorHandler(void *data, const struct _xmlError *error)
 {
 	PgXmlErrorContext *xmlerrcxt = (PgXmlErrorContext *) data;
 	xmlParserCtxtPtr ctxt = (xmlParserCtxtPtr) error->ctxt;