Actually, hopefully, you are bunding postgresql + cygwin + whatever other
binaries + *the sources to same* since this is a GPLed project, meaning
that you have to provide sources for the binaries that you distribute
as per the GPL.
No source code is modified/recompiled. I'm just providing a convenience
packaging. COPYING + the BSD license (for Postgres) is included, plus
I'm informing in the README that Cygwin is GPL'ed, and to get the source
one should go to http://www.cygwin.com/. I believe that is sufficient?
(since no source code is modified anyway).
Unfortunately, no, it's not sufficient. The GPL doesn't have a "no
source code is modified" clause. For the cygwin DLL, and any of the
utilities that come with it, you have to adhere to the GPL which
means that the source code has to be provided.