The attached patch fixes a longstanding problem with the Gtk+ build of 
emacs in Cygwin.  The problem is described in etc/PROBLEMS ("Emacs 
compiled with Gtk+ crashes on startup on Cygwin"), along with a 
workaround.  The patch simply incorporates that workaround into the 
emacs code.  I tried to do this so that the Cygwin-specific part is 
hidden in src/s/cygwin.h; it's conceivable that there are other systems 
where something similar would be useful.

The patch also removes the description of the problem from etc/PROBLEMS 
and removes a configuration warning.

Please apply the patch if it's OK, or tell me how to improve it.

Thanks.

Ken