bug#19909: [PATCH] Error out if with-file-notification=w32 is specified on cygwin

[Eli Zaretskii]

> From: Robert Pluim <rpluim@gmail.com>
> Date: Fri, 20 Feb 2015 17:44:30 +0100
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> From: Robert Pluim <rpluim@gmail.com>
> >> Date: Fri, 20 Feb 2015 16:46:48 +0100
> >> 
> >> >> I don't think adding w32.c into the build on cygwin is going to work.
> >> >
> >> > Because of the above, or because of something else?
> >> 
> >> Because (perhaps mistakenly) I think that calling emacs code that
> >> assumes it's running under Windows native will not interact well with
> >> emacs code that's running under cygwin.
> >
> > Sorry, maybe I'm confused, but isn't your Cygwin build configured
> > "--with-w32"?  If so, it already uses some of the Windows native code.
> 
> Yes, but only the bits relevant to the GUI. I don't know what the rest
> of it does :)

Most of native Windows code in Emacs is related to GUI.  That includes
drawing GUI frames and accepting input from the Windows message queue;
both are used by the Cygwin build --with-w32.

The rest is emulation of Posix functions, which Cygwin doesn't need.