fix imports to work with GHC 8.10

Also ended up taking out the conditional imports to support GHC 7.10,
since with the rearranged GHC APΙ imports it definitely wouldn't
anymore. If I identified the point where the changes happend between
8.0 and 8.10, could probably maintain support for all versions in between.

src/TypeNatSolver.hs

@@ -4,14 +4,13 @@ module TypeNatSolver (plugin) where
 
 import Type      ( Type, Kind, TyVar, eqType
                  , getTyVar_maybe, isNumLitTy, splitTyConApp_maybe
-                 , getEqPredTys, mkTyConApp, mkNumLitTy
-#if __GLASGOW_HASKELL__ <= 710
-                 , mkEqPred
-#else
-                 , mkPrimEqPred
-#endif
-                 , typeKind, classifyPredType, PredTree(..), EqRel(..)
-                 , getTyVar_maybe, getEqPredTys_maybe
+                 , mkTyConApp, mkNumLitTy
+                 , typeKind
+                 , getTyVar_maybe
+                 )
+import Predicate ( getEqPredTys, getEqPredTys_maybe
+                 , mkPrimEqPred, classifyPredType
+                 , Pred(..), EqRel(..)
                  )
 import TyCon     ( TyCon )
 import TcEvidence ( EvTerm(..) )
@@ -21,10 +20,10 @@ import OccName   ( occNameString )
 import Var       ( tyVarName )
 import TcPluginM ( TcPluginM, tcPluginIO, tcPluginTrace )
 import TcRnMonad ( TcPlugin(..), TcPluginResult(..)
-                 , Ct(..), CtEvidence(..), CtLoc, ctLoc, ctPred
-                 , mkNonCanonical, isTouchableTcM, unsafeTcPluginTcM
-                 )
-import TcRnTypes ( isDerivedCt )
+                 , isTouchableTcM, unsafeTcPluginTcM )
+import Constraint ( Ct(..), CtEvidence(..), CtLoc, ctLoc, ctPred
+                  , mkNonCanonical, isDerivedCt
+                  )
 import Plugins    ( CommandLineOption, defaultPlugin, Plugin(..) )
 
 import TcTypeNats ( typeNatAddTyCon
@@ -33,14 +32,10 @@ import TcTypeNats ( typeNatAddTyCon
                   , typeNatLeqTyCon
                   )
 import TysWiredIn ( typeNatKindCon
-#if __GLASGOW_HASKELL__ <= 710
-                  , promotedBoolTyCon
-#else
                   , boolTyCon
-#endif
                   , promotedFalseDataCon, promotedTrueDataCon
                   )
-import TrieMap    ( TypeMap, emptyTypeMap, lookupTypeMap, extendTypeMap )
+import CoreMap    ( TypeMap, emptyTypeMap, lookupTypeMap, extendTypeMap )
 
 import Outputable
 
@@ -586,7 +581,6 @@ type NewVarDecls  = Map String (Type,Ty)
 
 instance Monad ImportM where
   return a     = Imp (\s -> (a, s, Map.empty))
-  fail err     = panic err
   Imp m >>= k  = Imp (\s -> let (a,s1,ds1) = m s
                                 Imp m1     = k a
                                 (b,s2,ds2) = m1 s1