Bootstrap: Revert [38399] as it's broken /build/ and subsequently core.svn.wordpress.org.

The generated classmaps reference `/src/` files and operates in the assumption that the base directory is one level above `wp-settings.php`, which it isn't after our build processes are run.

See #36335


git-svn-id: https://develop.svn.wordpress.org/trunk@38402 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/pluggable.php

@@ -211,6 +211,7 @@ function wp_mail( $to, $subject, $message, $headers = '', $attachments = array()
 	// (Re)create it, if it's gone missing
 	if ( ! ( $phpmailer instanceof PHPMailer ) ) {
 		require_once ABSPATH . WPINC . '/class-phpmailer.php';
+		require_once ABSPATH . WPINC . '/class-smtp.php';
 		$phpmailer = new PHPMailer( true );
 	}