haskell: preserve overrideScope on override

We want code such as `(pkg.override {}).overrideScope (self: super: {})` to
work. This didn't work before, since `override` will call the original package
again, and the attribute `overideScope`, which `callPackageWithScope` added,
wasn't added again. The fix for this is to modify the package function itself
to include the `callPackageWithScope` attribute, so it'll be re-added whenever
the function is overriden for with arguments.

There is a small problem here though: since callPackage uses some magic
(`builtins.functionArgs`) to determine the auto-arguments of a function, we
can't just write `callPackageWith scope drvScope`, since
`builtins.functionArgs drvScope` will be `{}`. To fix this, we implement our own
`callPackageWith`.

fixes NixOS/nixpkgs#7953

pkgs/development/haskell-modules/default.nix

@@ -39,9 +39,15 @@ let
         mkDerivation = drv: args.mkDerivation (drv // f drv);
       });
 
-      callPackageWithScope = scope: drv: args: (stdenv.lib.callPackageWith scope drv args) // {
-        overrideScope = f: callPackageWithScope (mkScope (fix (extend scope.__unfix__ f))) drv args;
-      };
+      callPackageWithScope = scope: fn: args:
+        let
+          drv = if builtins.isFunction fn then fn else import fn;
+          auto = builtins.intersectAttrs (builtins.functionArgs drv) scope;
+          drvScope = args: drv args // { 
+            overrideScope = f: 
+              callPackageWithScope (mkScope (fix (extend scope.__unfix__ f))) drv args;
+          };
+        in stdenv.lib.makeOverridable drvScope (auto // args);
 
       mkScope = scope: pkgs // pkgs.xlibs // pkgs.gnome // scope;
       defaultScope = mkScope self;