Fixes for GHC 8.4.1 compatibility

* In GHC 8.4.1, the operator <> has become a method of the Semigroup class
  and is exported from the Prelude. This is unfortunate, since <> is also
  exported from the standard library module Text.PrettyPrint, so in any
  module that defines a pretty printer, there is likely to be an ambiguity.

  This affects ~18 modules in GF. Solution:

    import Prelude hiding (<>)

  This works also in older versions of GHC, since GHC does't complain if
  you hide something that doesn't exists.

* In GHC 8.4.1, Semigroup has become a superclass of Monoid. This means
  that anywhere you define an instance of the Monoid class you also have to
  define an instance in the Semigroup class.

  This affects Data.Binary.Builder in GF. Solution: conditionally define
  a Semigroup instance if compiling with base>=4.11 (ghc>=8.4.1)

src/compiler/GF/Command/Commands.hs

@@ -3,7 +3,7 @@ module GF.Command.Commands (
   PGFEnv,HasPGFEnv(..),pgf,mos,pgfEnv,pgfCommands,
   options,flags,
   ) where
-import Prelude hiding (putStrLn)
+import Prelude hiding (putStrLn,(<>)) -- GHC 8.4.1 clash with Text.PrettyPrint
 
 import PGF
 

src/compiler/GF/Command/Commands2.hs

@@ -3,7 +3,7 @@ module GF.Command.Commands2 (
   PGFEnv,HasPGFEnv(..),pgf,concs,pgfEnv,emptyPGFEnv,pgfCommands,
   options, flags,
   ) where
-import Prelude hiding (putStrLn)
+import Prelude hiding (putStrLn,(<>)) -- GHC 8.4.1 clash with Text.PrettyPrint
 
 import PGF2
 import qualified PGF as H

src/compiler/GF/Compile/CheckGrammar.hs

@@ -21,6 +21,7 @@
 -----------------------------------------------------------------------------
 
 module GF.Compile.CheckGrammar(checkModule) where
+import Prelude hiding ((<>)) -- GHC 8.4.1 clash with Text.PrettyPrint
 
 import GF.Infra.Ident
 import GF.Infra.Option

src/compiler/GF/Compile/Compute/ConcreteNew.hs

@@ -5,6 +5,7 @@ module GF.Compile.Compute.ConcreteNew
             normalForm,
             Value(..), Bind(..), Env, value2term, eval, vapply
            ) where
+import Prelude hiding ((<>)) -- GHC 8.4.1 clash with Text.PrettyPrint
 
 import GF.Grammar hiding (Env, VGen, VApp, VRecType)
 import GF.Grammar.Lookup(lookupResDefLoc,allParamValues)

src/compiler/GF/Compile/TypeCheck/RConcrete.hs

@@ -1,5 +1,6 @@
 {-# LANGUAGE PatternGuards #-}
 module GF.Compile.TypeCheck.RConcrete( checkLType, inferLType, computeLType, ppType ) where
+import Prelude hiding ((<>)) -- GHC 8.4.1 clash with Text.PrettyPrint
 
 import GF.Infra.CheckM
 import GF.Data.Operations

src/compiler/GF/CompileInParallel.hs

@@ -1,6 +1,6 @@
 -- | Parallel grammar compilation
 module GF.CompileInParallel(parallelBatchCompile) where
-import Prelude hiding (catch)
+import Prelude hiding (catch,(<>)) -- GHC 8.4.1 clash with Text.PrettyPrint
 import Control.Monad(join,ap,when,unless)
 import Control.Applicative
 import GF.Infra.Concurrency

src/compiler/GF/Grammar/Printer.hs

@@ -22,6 +22,7 @@ module GF.Grammar.Printer
            , ppMeta
            , getAbs
            ) where
+import Prelude hiding ((<>)) -- GHC 8.4.1 clash with Text.PrettyPrint
 
 import GF.Infra.Ident
 import GF.Infra.Option

src/compiler/GF/Haskell.hs

@@ -1,6 +1,7 @@
 -- | Abstract syntax and a pretty printer for a subset of Haskell
 {-# LANGUAGE DeriveFunctor #-}
 module GF.Haskell where
+import Prelude hiding ((<>)) -- GHC 8.4.1 clash with Text.PrettyPrint
 import GF.Infra.Ident(Ident,identS)
 import GF.Text.Pretty
 

src/compiler/GF/Infra/CheckM.hs

@@ -18,6 +18,7 @@ module GF.Infra.CheckM
 	   checkIn, checkInModule, checkMap, checkMapRecover,
            parallelCheck, accumulateError, commitCheck,
 	  ) where
+import Prelude hiding ((<>)) -- GHC 8.4.1 clash with Text.PrettyPrint
 
 import GF.Data.Operations
 --import GF.Infra.Ident

src/compiler/GF/Infra/Location.hs

@@ -1,5 +1,6 @@
 -- | Source locations
 module GF.Infra.Location where
+import Prelude hiding ((<>)) -- GHC 8.4.1 clash with Text.PrettyPrint
 import GF.Text.Pretty
 
 -- ** Source locations

src/compiler/GF/Speech/GSL.hs

@@ -7,6 +7,7 @@
 -----------------------------------------------------------------------------
 
 module GF.Speech.GSL (gslPrinter) where
+import Prelude hiding ((<>)) -- GHC 8.4.1 clash with Text.PrettyPrint
 
 --import GF.Data.Utilities
 import GF.Grammar.CFG

src/compiler/GF/Speech/JSGF.hs

@@ -11,6 +11,7 @@
 -----------------------------------------------------------------------------
 
 module GF.Speech.JSGF (jsgfPrinter) where
+import Prelude hiding ((<>)) -- GHC 8.4.1 clash with Text.PrettyPrint
 
 --import GF.Data.Utilities
 import GF.Infra.Option

src/compiler/GF/Speech/SRGS_ABNF.hs

@@ -18,6 +18,7 @@
 -----------------------------------------------------------------------------
 
 module GF.Speech.SRGS_ABNF (srgsAbnfPrinter, srgsAbnfNonRecursivePrinter) where
+import Prelude hiding ((<>)) -- GHC 8.4.1 clash with Text.PrettyPrint
 
 --import GF.Data.Utilities
 import GF.Infra.Option

src/runtime/haskell-bind/PGF2.hsc

@@ -82,7 +82,7 @@ module PGF2 (-- * PGF
              LiteralCallback,literalCallbacks
             ) where
 
-import Prelude hiding (fromEnum)
+import Prelude hiding (fromEnum,(<>)) -- GHC 8.4.1 clash with Text.PrettyPrint
 import Control.Exception(Exception,throwIO)
 import Control.Monad(forM_)
 import System.IO.Unsafe(unsafePerformIO,unsafeInterleaveIO)

src/runtime/haskell/Data/Binary/Builder.hs

@@ -100,6 +100,11 @@ newtype Builder = Builder {
         runBuilder :: (Buffer -> [S.ByteString]) -> Buffer -> [S.ByteString]
     }
 
+#if MIN_VERSION_base(4,11,0)
+instance Semigroup Builder where
+  (<>) = append
+#endif
+
 instance Monoid Builder where
     mempty  = empty
     {-# INLINE mempty #-}

src/runtime/haskell/PGF/ByteCode.hs

@@ -2,7 +2,7 @@ module PGF.ByteCode(Literal(..),
                     CodeLabel, Instr(..), IVal(..), TailInfo(..),
                     ppLit, ppCode, ppInstr
                    ) where
-
+import Prelude hiding ((<>)) -- GHC 8.4.1 clash with Text.PrettyPrint
 import PGF.CId
 import Text.PrettyPrint
 

src/runtime/haskell/PGF/Macros.hs

@@ -1,4 +1,5 @@
 module PGF.Macros where
+import Prelude hiding ((<>)) -- GHC 8.4.1 clash with Text.PrettyPrint
 
 import PGF.CId
 import PGF.Data

src/runtime/haskell/PGF/Printer.hs

@@ -1,5 +1,6 @@
 {-# LANGUAGE FlexibleContexts #-}
 module PGF.Printer (ppPGF,ppCat,ppFId,ppFunId,ppSeqId,ppSeq,ppFun) where
+import Prelude hiding ((<>)) -- GHC 8.4.1 clash with Text.PrettyPrint
 
 import PGF.CId
 import PGF.Data

src/runtime/haskell/PGF/VisualizeTree.hs

@@ -23,6 +23,7 @@ module PGF.VisualizeTree
              , gizaAlignment
              , conlls2latexDoc
              ) where
+import Prelude hiding ((<>)) -- GHC 8.4.1 clash with Text.PrettyPrint
 
 import PGF.CId (wildCId,showCId,ppCId,mkCId) --CId,pCId,
 import PGF.Data