bug#26459: 26.0.50; loaddefs.el is regenerated after each "git pull"

[Eli Zaretskii]

> From: Glenn Morris <rgm@gnu.org>
> Cc: 26459@debbugs.gnu.org,  eggert@cs.ucla.edu
> Date: Wed, 12 Apr 2017 11:58:27 -0400
> 
> 
> IIUC 440bafe has made this much slower by defeating the prior "only
> update where needed" aspect of this.

440bafe made the rule generate the loaddefs in a temporary file.
Would it help to copy loaddefs.el into loaddefs.tmp before running
batch-update-autoloads?

Still, I don't see why the time stamp of loaddefs.el should be
ignored.