Fix build with stack

Author: jhrcek

haskell-language-server.cabal

@@ -389,9 +389,6 @@ library hls-eval-plugin
     , unliftio
     , unordered-containers
 
-  if flag(pedantic)
-    ghc-options: -Wwarn=redundant-constraints
-
   default-extensions:
     DataKinds
 
@@ -1683,6 +1680,11 @@ library
 
   default-extensions: DataKinds
 
+  if flag(pedantic)
+    ghc-options:
+      --See Note [unused-packages]
+      -Wwarn=unused-packages
+
 executable haskell-language-server
   import:           defaults
                   , warnings