This reverts commit d170c98d13.
niksnut argues that we need smaller system closures, not bigger.
So users facing the trouble of getting gcc rebuilds after nix-collect-garbage
for any minimal nixos configuration change should use other means of
not losing the stdenv output.
One way is to keep one somewhere: nix-build -A stdenv -o stdenv '<nixpkgs>'.
Another may be to use nix.conf options like gc-keep-outputs, gc-keep-derivations
or env-keep-derivations.
21dd114f82