eclipses: 2021-09 -> 2021-12
the .eclipseproduct file bundled with 2021-12 mistakenly still saysversion=4.21.0, so tweak build-eclipse.nix to stop relying on it fornow.
authored by Matt McHenry and committed by Robert Helgesson 4 years ago 8a7561ec dc6a5c46