Docs: Document the $xmlrpc_logging global in logIO().

Follow-up to [1348], [19935].

Props viralsampat, upadalavipul, sabernhardt.
See #60021.
Built from https://develop.svn.wordpress.org/trunk@57752


git-svn-id: http://core.svn.wordpress.org/trunk@57253 1a063a9b-81f0-0310-95a4-ce76da25c4cd

xmlrpc.php

@@ -91,10 +91,13 @@ exit;
 /**
  * logIO() - Writes logging info to a file.
  *
+ * @since 1.2.0
  * @deprecated 3.4.0 Use error_log()
  * @see error_log()
  *
- * @param string $io Whether input or output
+ * @global int|bool $xmlrpc_logging Whether to enable XML-RPC logging.
+ *
+ * @param string $io  Whether input or output.
  * @param string $msg Information describing logging reason.
  */
 function logIO( $io, $msg ) {