Automatically set distributed build's supportedFeatures based on that host's actual config.

Previously, we had two copies of the supported features for each host.

nix/configuration/flake.nix

@@ -69,6 +69,8 @@
 
             this_nixos_config = self.nixosConfigurations."${hostname}";
 
+            all_nixos_configs = self.nixosConfigurations;
+
             pkgs-unoptimized = import nixpkgs-unoptimized {
               inherit (nodeConfig) system;
               hostPlatform.gcc.arch = "default";