bug#50666: 28.0.50; Fix native compilation on Cygwin

[Eli Zaretskii]

> Cc: akrl@sdf.org, Stromeko@nexgo.de, 50666@debbugs.gnu.org
> From: Ken Brown <kbrown@cornell.edu>
> Date: Thu, 23 Sep 2021 13:13:05 -0400
> 
> > My point is that maybe we should make that decision already, before
> > burning too much time and energy on it.
> 
> You might be right.  I wasn't aware of all the complications you mentioned 
> above.

It took us most of the last year to realize how tricky this stuff is.
We are still learning ;-)

> We still need to do something for 64-bit Cygwin.  Even though address 
> collisions 
> are unlikely they could still happen theoretically.  But there might be a 
> much 
> easier solution that doesn't necessarily require rebasing.  For example, 
> Achim 
> mentioned earlier the possibility of marking the eln as ASLR w/ high-entropy 
> and
> large address aware.

Isn't that the default of the 64-bit GNU ld on Windows?  Or does
Cygwin configure Binutils differently from MinGW?

If not, we can use native-comp-driver-options, by giving it a non-nil
value for Cygwin, to force this.