freshBootstrapTools.bootstrapTools: fix eval on darwin

```
error: undefined variable 'system'
       at /home/artturin/nixgits/my-nixpkgs/.worktree/1/pkgs/stdenv/darwin/make-bootstrap-tools.nix:213:32:

          212|
          213|   bootstrapTools = derivation {
             |                                ^
          214|     inherit system;

```

fixes eval of `freshBootstrapTools.bootstrapTools` in darwin repl

pkgs/stdenv/darwin/make-bootstrap-tools.nix

@@ -211,7 +211,7 @@ in rec {
   };
 
   bootstrapTools = derivation {
-    inherit system;
+    inherit (localSystem) system;
 
     name = "bootstrap-tools";
     builder = "${bootstrapFiles.tools}/bin/bash";