Fix build warnings introduced in #1165

crucible/src/Lang/Crucible/Backend.hs

@@ -36,6 +36,7 @@ obligations with a solver backend.
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE TypeOperators #-}
 {-# LANGUAGE ViewPatterns #-}
 module Lang.Crucible.Backend
   ( IsSymBackend(..)
@@ -118,7 +119,6 @@ import           Data.Sequence (Seq)
 import           Data.Set (Set)
 import qualified Prettyprinter as PP
 import           GHC.Stack
-import           System.IO
 
 import           Data.Parameterized.Map (MapF)
 
@@ -132,7 +132,6 @@ import           What4.Partial
 import           What4.ProgramLoc
 import           What4.Expr (GroundValue, GroundValueWrapper(..))
 import           What4.Solver
-import qualified What4.Solver.CVC5 as CVC5
 import qualified What4.Solver.Z3 as Z3
 
 import qualified Lang.Crucible.Backend.AssumptionStack as AS