gerbil-unstable: 2019-08-11 -> 2019-11-10
gerbil-unstable: 2019-08-11 -> 2019-11-10

Also, build with gambit rather than gambit-unstable, because of, well,
instability in the current gambit-unstable.

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs