Some package I am trying to build with cabal causes cabal to try to install unix-2.6.0.0 . This fails with the following errors:

[35 of 38] Compiling System.Posix.Signals ( dist/build/System/Posix/Signals.hs, dist/build/System/Posix/Signals.o )
/var/folders/_c/4n2x0zfx7mx5gk_46pdxn3pm0000gn/T/ghc30459_0/ghc30459_0.c: In function ‘ghc_wrapper_dtUw_sigismember’:

/var/folders/_c/4n2x0zfx7mx5gk_46pdxn3pm0000gn/T/ghc30459_0/ghc30459_0.c:8:0:
     warning: dereferencing ‘void *’ pointer

/var/folders/_c/4n2x0zfx7mx5gk_46pdxn3pm0000gn/T/ghc30459_0/ghc30459_0.c:8:0:
     error: void value not ignored as it ought to be
/var/folders/_c/4n2x0zfx7mx5gk_46pdxn3pm0000gn/T/ghc30459_0/ghc30459_0.c: In function ‘ghc_wrapper_dtUF_sigfillset’:

/var/folders/_c/4n2x0zfx7mx5gk_46pdxn3pm0000gn/T/ghc30459_0/ghc30459_0.c:10:0:
     warning: dereferencing ‘void *’ pointer

/var/folders/_c/4n2x0zfx7mx5gk_46pdxn3pm0000gn/T/ghc30459_0/ghc30459_0.c:10:0:
     error: invalid use of void expression
/var/folders/_c/4n2x0zfx7mx5gk_46pdxn3pm0000gn/T/ghc30459_0/ghc30459_0.c: In function ‘ghc_wrapper_dtUR_sigdelset’:

/var/folders/_c/4n2x0zfx7mx5gk_46pdxn3pm0000gn/T/ghc30459_0/ghc30459_0.c:12:0:
     warning: dereferencing ‘void *’ pointer

/var/folders/_c/4n2x0zfx7mx5gk_46pdxn3pm0000gn/T/ghc30459_0/ghc30459_0.c:12:0:
     error: invalid use of void expression
Failed to install unix-2.6.0.0

This seems to be a recent problem for me, so it may be due to some software updates for mac os x. I am running os x version 10.8.2 build 12c60. I have XCode version 4.5.1 with the "Command Line Tools" installed. I installed ghc from the haskell-platform after updating the os x and xcode (and command line tools).