BUG #8254: On cygwin DLLWRAP produces buggy shared lib

The following bug has been logged on the website:

Bug reference:      8254
Logged by:          Marco Atzeri
Email address:      marco.atzeri@gmail.com
PostgreSQL version: 9.2.4
Operating system:   Windows / Cygwin build
Description:

The usage of dllwrap (deprecated on cygwin) produces buggy shared lib
causing segfault of psql after rebase.


Reported here:
http://cygwin.com/ml/cygwin/2013-03/msg00022.html
http://www.cygwin.com/ml/cygwin/2013-03/msg00032.html
http://www.cygwin.com/ml/cygwin/2013-03/msg00134.html


The patch to switch from dllwrap and dlltool to only gcc, was already
attached here:


http://www.postgresql.org/message-id/51B59794.3000500@gmail.com


Also added DLL versioning, following cygwin scheme.