Rewrite Rules: Check if `$wp_rewrite->flush_rules()` is callable before calling it in `flush_rewrite_rules()`.

Props bsetiawan88, markjaquith.
Fixes #47087.
Built from https://develop.svn.wordpress.org/trunk@45699


git-svn-id: http://core.svn.wordpress.org/trunk@45510 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/rewrite.php

@@ -273,7 +273,10 @@ function add_feed( $feedname, $function ) {
  */
 function flush_rewrite_rules( $hard = true ) {
 	global $wp_rewrite;
+
+	if ( is_callable( array( $wp_rewrite, 'flush_rules' ) ) ) {
 		$wp_rewrite->flush_rules( $hard );
+	}
 }
 
 /**

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.3-alpha-45698';
+$wp_version = '5.3-alpha-45699';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.