Cabal shouldn't try to build split-objs when ghc reports it does not support it

(Imported from [Trac #421](http://hackage.haskell.org/trac/hackage/ticket/421), reported by @dcoutts on 2008-12-01)

It is possible to build ghc without support for object splitting. In such a case Cabal should refuse to work if the user enables split objs.

All one has to do is to parse the output of ghc --info (which is in a Read/Show format).

See also #24.