Fix #1507 by running postBuild hook in setup build (#1519)

* Includes very temporary work around for CI issue

Author: hamishmack

builder/setup-builder.nix

@@ -82,7 +82,7 @@ let
           fi
         done
         [ -f ./Setup ] || (echo Failed to build Setup && exit 1)
-        runHook preBuild
+        runHook postBuild
       '';
 
       installPhase = ''

overlays/hackage-quirks.nix

@@ -25,6 +25,16 @@ in { haskell-nix = prev.haskell-nix // {
       ];
     };
 
+    # TODO remove this when `dependent-sum-0.7.1.0` constraint on `some` has been updated.
+    # See https://github.com/haskell/haskell-language-server/issues/2969
+    # and https://github.com/obsidiansystems/dependent-sum/issues/71
+    haskell-language-server = {
+      cabalProject = ''
+        packages: .
+        constraints: dependent-sum >=0.7.1.0
+      '';
+    };
+
     lsp-test = {
       cabalProject = ''
         packages: .