release-lib.nix: Make the set of supported platforms an argument

pkgs/top-level/release-cross.nix

@@ -1,4 +1,4 @@
-with (import ./release-lib.nix);
+with import ./release-lib.nix { supportedSystems = []; };
 let
   nativePlatforms = linux;
 

pkgs/top-level/release-lib.nix

@@ -1,3 +1,5 @@
+{ supportedSystems }:
+
 rec {
 
   # Ensure that we don't build packages marked as unfree.
@@ -8,10 +10,6 @@ rec {
   pkgs = allPackages { system = "x86_64-linux"; };
 
 
-  # The platforms for which we build Nixpkgs.
-  supportedSystems = [ "x86_64-linux" "i686-linux" "x86_64-darwin" "x86_64-freebsd" "i686-freebsd" ];
-
-
   /* !!! Hack: poor man's memoisation function.  Necessary to prevent
      Nixpkgs from being evaluated again and again for every
      job/platform pair. */

pkgs/top-level/release.nix

@@ -11,9 +11,11 @@
 
 { nixpkgs ? { outPath = (import ./all-packages.nix {}).lib.cleanSource ../..; revCount = 1234; shortRev = "abcdef"; }
 , officialRelease ? false
+, # The platforms for which we build Nixpkgs.
+  supportedSystems ? [ "x86_64-linux" "i686-linux" "x86_64-darwin" "x86_64-freebsd" "i686-freebsd" ]
 }:
 
-with import ./release-lib.nix;
+with import ./release-lib.nix { inherit supportedSystems; };
 
 let