fix newer ghc: Don't try to be backwards compatible

src/compiler/GF/Data/BacktrackM.hs

@@ -69,6 +69,8 @@ instance Monad (BacktrackM s) where
     return a   = BM (\c s b -> c a s b)
     BM m >>= k = BM (\c s b -> m (\a s b -> unBM (k a) c s b) s b)
 	where unBM (BM m) = m
+
+instance MonadFail (BacktrackM s) where
     fail _ = mzero
 
 instance Functor (BacktrackM s) where

src/compiler/GF/Data/ErrM.hs

@@ -16,10 +16,6 @@ module GF.Data.ErrM where
 
 import Control.Monad (MonadPlus(..),ap)
 import Control.Applicative
-#if !MIN_VERSION_base(4,11,0)
--- Control.Monad.Fail import is redundant since GHC 8.8.1
-import qualified Control.Monad.Fail as Fail
-#endif
 
 -- | Like 'Maybe' type with error msgs
 data Err a = Ok a | Bad String
@@ -40,17 +36,8 @@ instance Monad Err where
   Ok a  >>= f = f a
   Bad s >>= f = Bad s
 
-#if !(MIN_VERSION_base(4,11,0))
+instance MonadFail Err where
   fail        = Bad
-#endif
-
-instance Fail.MonadFail Err where
-  fail        = Bad
-
--- Control.Monad.Fail import will become redundant in GHC 8.8+
-import qualified Control.Monad.Fail as Fail
-
-