fix build and tests for ghc >8.6

src/Language/Wasm/Validate.hs

@@ -16,8 +16,8 @@ import qualified Data.Set as Set
 import Data.List (foldl')
 import qualified Data.Text.Lazy as TL
 import Data.Maybe (fromMaybe, maybeToList, catMaybes)
-import Data.Monoid ((<>))
 import Numeric.Natural (Natural)
+import Prelude hiding ((<>))
 
 import Control.Monad (foldM)
 import Control.Monad.Reader (ReaderT, runReaderT, withReaderT, ask)
@@ -52,6 +52,10 @@ data ValidationError =
 
 type ValidationResult = Either ValidationError ()
 
+-- semigroup definition for Either a b is in conflict with my ad-hoc instance
+-- to keep an old code Prelude version is hidden and redefined locally
+(<>) = mappend
+
 instance Monoid ValidationResult where
     mempty = Right ()
     mappend (Right ()) vr = vr