Coding Standards: Fix instances of WordPress.PHP.NoSilencedErrors.Discouraged.

Noteable changes:
- The `magic_quotes_runtime` and `magic_quotes_sybase` settings were removed in PHP 5.4, so no longer need to be set.
- Some functions that use external libraries can generate errors that can't be tested for, so are globally allowed to silence errors.
- Quite a few functions would cause errors if `safe_mode` was set. This setting was removed in PHP 5.4.
- Only a handful of `header()` calls needed corresponding `headers_sent()` checks for unit tests to pass, but more may need to be added as the nightlies builds are tested.

See #46732.


git-svn-id: https://develop.svn.wordpress.org/trunk@45611 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/cron.php

@@ -677,11 +677,10 @@ function spawn_cron( $gmt_time = 0 ) {
 		echo ' ';
 
 		// flush any buffers and send the headers
-		while ( @ob_end_flush() ) {
-		}
+		wp_ob_end_flush_all();
 		flush();
 
-		WP_DEBUG ? include_once( ABSPATH . 'wp-cron.php' ) : @include_once( ABSPATH . 'wp-cron.php' );
+		include_once( ABSPATH . 'wp-cron.php' );
 		return true;
 	}