bug#48117: 28.0.50; Update of loaddefs.el during normal build is unreliable

[Eli Zaretskii]

> Date: Fri, 30 Apr 2021 19:08:48 +0000
> From: Gregory Heytings <gregory@heytings.org>
> cc: 48117@debbugs.gnu.org
> 
> Note that, as I said, this won't work without keeping ldefs-boot.el up to 
> date.

We (read: Glenn) already do.  You can see that in "git log".