Refer to GHC when acting on GHC quirks

Author: HuwCampbell

optparse-applicative.cabal

@@ -121,7 +121,7 @@ library
   if flag(process)
     build-depends:     process                         >= 1.0   && < 1.7
 
-  if !impl(ghc >= 8) && !impl(mhs)
+  if impl(ghc < 8)
     build-depends:     semigroups                      >= 0.10  && < 0.21
                      , fail                            == 4.9.*
 

src/Options/Applicative/BashCompletion.hs

@@ -14,7 +14,7 @@ module Options.Applicative.BashCompletion
 
 import Control.Applicative
 import Prelude
-#if !defined(__MHS__)
+#if !MIN_VERSION_base(4,16,0)
 import Data.Foldable ( asum )
 #endif
 
@@ -232,7 +232,7 @@ words.
 Tab characters separate items from descriptions.
 -}
 
--- | Generated fish shell completion script 
+-- | Generated fish shell completion script
 fishCompletionScript :: String -> String -> String
 fishCompletionScript prog progn = unlines
   [ " function _" ++ progn

src/Options/Applicative/Help/Core.hs

@@ -1,4 +1,3 @@
-{-# LANGUAGE CPP #-}
 module Options.Applicative.Help.Core (
   cmdDesc,
   briefDesc,