hosts/modules: put builder back in a separate file

Signed-off-by: Amneesh Singh <natto@weirdnatto.in>

hosts/modules/x86builder.nix

@@ -0,0 +1,16 @@
+{ config, ... }:
+{
+  nix = {
+    extraOptions = ''
+      builders-use-substitutes = true
+    '';
+    buildMachines = [{
+      hostName = "satori";
+      systems = [ "x86_64-linux" "aarch64-linux" ];
+      maxJobs = 4;
+      speedFactor = 2;
+      supportedFeatures = [ "nixos-test" "benchmark" "big-parallel" "kvm" ];
+    }];
+    distributedBuilds = true;
+  };
+}