[Yhc] Adding base libraries to yhc

[Neil Mitchell]

Hi


> I would think that nowadays the appropriate way to specify this is to
> put {-# LANGUAGE CPP #-} at the beginning of each file that needs it? see
> http://www.haskell.org/ghc/docs/latest/html/users_guide/pragmas.html#language-pragma
> "This allows language extensions to be enabled in a portable way. It is
> the intention that all Haskell compilers support the LANGUAGE pragma
> with the same syntax, although not all extensions are supported by all
> compilers, of course." ...

We have pragmas, so adding that shouldn't be too hard. If someone
opens a bug for it, we won't forget.

However for the base libraries, we want the minimal set of changes
required to the code, to make it easier to get the changes integrated
back in. GHC and Hugs both just preprocess all the base package with
flags, we should do the same.

Personally I think adding pragma's at the top of each file is a much
better method, but for the base library if we want to do this we
should probably ping libraries@ and see what people think - my guess
is most will say no.

Thanks

Neil