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

[Eli Zaretskii]

> From: Andreas Schwab <schwab@linux-m68k.org>
> Cc: Eli Zaretskii <eliz@gnu.org>,  48117@debbugs.gnu.org
> Date: Fri, 30 Apr 2021 17:59:45 +0200
> 
> On Apr 30 2021, Glenn Morris wrote:
> 
> > always regenerate loaddefs, but using a temporary file name for the
> > main loaddefs.
> > use build-aux/move-if-change to only replace the real loaddefs file if
> > there have been changes.
> 
> That's already what batch-update-autoloads does.

Judging by the results, that's not so.  Specifically,
batch-update-autoloads doesn't regenerate _all_ of the loaddefs.el,
only some of its part(s).