bug#62462: 30.0.50; Implement list-system-processes on Cygwin

[Eli Zaretskii]

> Date: Sun, 26 Mar 2023 10:25:41 -0400
> From: Ken Brown <kbrown@cornell.edu>
> 
> I've just discovered, because of the failure of all the proced tests,
> that list-system-processes has never been implemented on Cygwin (i.e.,
> it always returns nil).  All that's needed to fix this is to tell Emacs
> that Cygwin has a /proc filesystem.
> 
> Patch attached, with a place holder for the bug number.  With this patch
> applied, all of the proced tests pass.  OK to push to master?

Yes, thanks.