Only language extensions not active when `-XHaskell2010` is enabled are
declared, this way we can drop many redundant
`{-# LANGUAGE ForeignFunctionInterface #-}` occurences. This commit also
removes/replaces some `{-# OPTIONS_GHC -XRecordWildCards #-}` pragmas.

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>

and remove code to support older versions

The new module System.Posix.ByteString provides exactly the same API
as System.Posix, except that:

  - There is a new type: RawFilePath = ByteString

  - All functions mentioning FilePath in the System.Posix API
    use RawFilePath in the System.Posix.ByteString API

  - RawFilePaths are not subject to Unicode locale encoding and
    decoding, unlike FilePaths.  They are the exact bytes passed to and
    returned from the underlying POSIX API.

  - Similarly for functions that deal in environment
    strings (System.Posix.Env): these use untranslated ByteStrings
    in System.Posix.Environment

  - There is a new function

     System.Posix.ByteString.getArgs :: [ByteString]

    returning the raw untranslated arguments as passed to exec() when
    the program was started.

Export Module (abstractly), otherwise the user is unable to write
signatures involving this type. Improves Haddock hyperlinks, too.

- move System.DL to System.Posix.DynamicLinker
- take ownership

There's a compiler warning when passing the 'const char*' result from
dlerror() to peekCString (discarded qualifier). Does an FFI-expert know
how to get rid of this warning?

Import System/DL*