patch applied (ghc): Only make the Windows installer if ISCC is set

[Ian Lynagh]

Sat Oct 10 09:02:46 PDT 2009  Ian Lynagh <igloo at earth.li>
  * Only make the Windows installer if ISCC is set
  Now that we make bindists during validate, we can't assume that ISCC
  is available.

    M ./ghc.mk +4

View patch online:
http://darcs.haskell.org/ghc/_darcs/patches/20091010160246-3fd76-601041d8b79c1bff840bcbfff6796d9b2cfbfa3e.gz