I think it's the Cygwin project. We are only responsible for ensuring
that it builds and runs correctly on Cygwin. But I'm sure they'll
accept a patch if one of us sends it to them.
The real problem is keeping it up to date. Just updating it to 5.3.0
should be a matter of sending a patch, but keeping it up to date,
following up when things break etc is something that really requires
someone who actively uses CHICKEN from Cygwin.
For the foreseeable future I'll once again be running Chicken on Cygwin and building it myself, so I will definitely report if it breaks. However, I think it's enough to send Cygwin updates only for minor versions (5.3, 5.4, etc.) and security patches, not for every single patch that's ever issued.