Extract toolchain build from the CI

nix/nix.conf

@@ -2,6 +2,3 @@ substituters = https://cache.nixos.org https://nix.web.deuxfleurs.fr
 trusted-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY= nix.web.deuxfleurs.fr:eTGL6kvaQn6cDR/F9lDYUIP9nCVR/kkshYfLDJf1yKs=
 max-jobs = auto
 cores = 4
-
-# required for containers
-sandbox = false

nix/toolchain.nix

@@ -0,0 +1,29 @@
+{
+  system ? builtins.currentSystem,
+}:
+
+with import ./common.nix;
+
+let
+  platforms = [
+    "x86_64-unknown-linux-musl"
+    "i686-unknown-linux-musl"
+    "aarch64-unknown-linux-musl"
+    "armv6l-unknown-linux-musleabihf"
+  ];
+  pkgsList = builtins.map (target: import pkgsSrc { 
+    inherit system; 
+    crossSystem = { config = target; };
+  }) platforms;
+  pkgsHost = import pkgsSrc {};
+  lib = pkgsHost.lib;
+  kaniko = (import ./kaniko.nix) pkgsHost;
+in 
+  lib.flatten (builtins.map (pkgs: [
+     pkgs.rustPlatform.rust.rustc
+     pkgs.rustPlatform.rust.cargo
+     pkgs.buildPackages.stdenv.cc
+  ]) pkgsList) ++ [
+    kaniko
+  ]
+