bug#50666: 28.0.50; Fix native compilation on Cygwin

[Eli Zaretskii]

> Cc: 50666@debbugs.gnu.org
> From: Ken Brown <kbrown@cornell.edu>
> Date: Sun, 19 Sep 2021 08:37:52 -0400
> 
> Cygwin could maintain a per-user database of *.eln files and their base 
> addresses.  (It already maintains a system database of this type.)  The each 
> time a new *.eln file is created, it could be rebased and added to the 
> database 
> before being loaded.

I don't think I understand: rebased and added how? manually?