haskell/with-packages-wrapper.nix: install "doc" outputs

We were previously just installing the "out" output which broke when
we recently changed to generating multiple outputs.

Fixes NixOS#76837

pkgs/development/haskell-modules/with-packages-wrapper.nix

@@ -1,4 +1,4 @@
-{ lib, stdenv, ghc, llvmPackages, packages, symlinkJoin, makeWrapper
+{ lib, stdenv, ghc, llvmPackages, packages, buildEnv, makeWrapper
 , withLLVM ? false
 , postBuild ? ""
 , ghcLibdir ? null # only used by ghcjs, when resolving plugins
@@ -51,12 +51,13 @@ let
                    ++ lib.optional stdenv.targetPlatform.isDarwin llvmPackages.clang);
 in
 if paths == [] && !withLLVM then ghc else
-symlinkJoin {
+buildEnv {
   # this makes computing paths from the name attribute impossible;
   # if such a feature is needed, the real compiler name should be saved
   # as a dedicated drv attribute, like `compiler-name`
   name = ghc.name + "-with-packages";
   paths = paths ++ [ghc];
+  extraOutputsToInstall = ["doc"];
   postBuild = ''
     . ${makeWrapper}/nix-support/setup-hook