bug#46790: 28.0.50; make install with native-comp branch

[Eli Zaretskii]

> From: Phil Sainty <psainty@orcon.net.nz>
> Date: Tue, 20 Apr 2021 21:33:45 +1200
> Cc: 46790@debbugs.gnu.org
> 
> Hi Thierry,
> 
> I suspect your bug has now been fixed in #44128.
> https://debbugs.gnu.org/cgi/bugreport.cgi?bug=44128

I think only as long as $(libdir) and $(libexecdir) keep their
relative locations.

We don't really support separate unsynchronized locations for the
various *dir variables used to install Emacs.  The official way of
moving the entire installation is by either specifying prefix= or by
DESTDIR=.