patch applied (ghc): Fix Trac #1037

[Simon Peyton Jones]

Sat Aug  4 10:44:20 PDT 2007  simonpj at microsoft.com
  * Fix Trac #1037
  
  It makes *sense* for a foreign import to have a zero-sized return, thus
  
    foreign import ccall foo :: Int -> State# RealWorld
  
  but it's not clear that it's useful, and it requires some back-end (a
  Hint for void types) to make it go right through. It's not clear that
  we really want this facility, so rather than fixing the code
  generator, I'm just making the construct illegal for now.
  

    M ./compiler/typecheck/TcType.lhs -7 +18