release.nix: pass missing parameter

Commit 5643714 introduced a tiny
bug, neglecting to pass the `pkgs` parameter to `release.nix`.

This bug went unnoticed because commit
e663518 had introduced a much larger
bug: an attribute collision resulted in `stdenvBootstrapTools` being
shadowed, and therefore never evaluated.  As a result, the missing
`pkgs` parameter did not lead to an error.

This commit passes the missing parameter so that fixing the
larger/earlier bug will not cause an eval failure.

pkgs/top-level/release.nix

@@ -167,7 +167,10 @@ let
             (system: {
               inherit
                 (import ../stdenv/linux/make-bootstrap-tools.nix {
-                  localSystem = { inherit system; };
+                  pkgs = import ../.. {
+                    localSystem = { inherit system; };
+                    crossSystem = { inherit system; };
+                  };
                 })
                 dist test;
             })