remove more things needed by GHC < 8.6

Trace/Hpc/Mix.hs

-{-# LANGUAGE CPP, Safe #-}
+{-# LANGUAGE Safe #-}
 ---------------------------------------------------------------
 -- Colin Runciman and Andy Gill, June 2006
 ---------------------------------------------------------------
@@ -21,11 +21,7 @@ import Data.List (intercalate)
 import Data.Maybe (catMaybes, fromMaybe)
 import Data.Time (UTCTime)
 import Data.Tree
-#if MIN_VERSION_base(4,6,0)
 import Text.Read (readMaybe)
-#else
-import Data.Char (isSpace)
-#endif
 
 import System.FilePath
 
@@ -36,13 +32,6 @@ import System.FilePath
 import Trace.Hpc.Util (HpcPos, insideHpcPos, Hash, HpcHash(..), catchIO)
 import Trace.Hpc.Tix
 
-#if !MIN_VERSION_base(4,6,0)
-readMaybe :: Read a => String -> Maybe a
-readMaybe s = case reads s of
-  [(x, s')] | all isSpace s' -> Just x
-  _                          -> Nothing
-#endif
-
 -- | 'Mix' is the information about a modules static properties, like
 -- location of Tix's in a file.
 --

Trace/Hpc/Tix.hs

-{-# LANGUAGE CPP, Safe, DeriveGeneric, StandaloneDeriving #-}
+{-# LANGUAGE Safe, DeriveGeneric, StandaloneDeriving #-}
 ------------------------------------------------------------
 -- Andy Gill and Colin Runciman, June 2006
 ------------------------------------------------------------

Trace/Hpc/Util.hs

 {-# LANGUAGE Safe, DeriveGeneric, StandaloneDeriving #-}
-
 -----------------------------------------
 -- Andy Gill and Colin Runciman, June 2006
 ------------------------------------------

hpc.cabal

@@ -26,7 +26,6 @@ source-repository head
 
 Library
     default-language: Haskell98
-    other-extensions: CPP
 
     exposed-modules:
         Trace.Hpc.Util