Merge pull request #15989 from mboes/stack-builder-tweaks

haskell.lib.buildStackProject: allow passing in a custom GHC version.

pkgs/development/haskell-modules/generic-stack-builder.nix

@@ -4,7 +4,8 @@ with stdenv.lib;
 
 { buildInputs ? []
 , extraArgs ? []
-, LD_LIBRARY_PATH ? ""
+, LD_LIBRARY_PATH ? []
+, ghc ? ghc
 , ...
 }@args:
 
@@ -22,7 +23,7 @@ stdenv.mkDerivation (args // {
     extraArgs;
 
   # XXX: workaround for https://ghc.haskell.org/trac/ghc/ticket/11042.
-  LD_LIBRARY_PATH = "${makeLibraryPath buildInputs}:${LD_LIBRARY_PATH}";
+  LD_LIBRARY_PATH = makeLibraryPath (LD_LIBRARY_PATH ++ buildInputs);
 
   preferLocalBuild = true;