Use pthread_kill on OS X too

Fixes signals004(threaded1,threaded2) on OS X 32.

rts/RtsUtils.c

@@ -272,7 +272,7 @@ heapCheckFail( void )
  * genericRaise(), rather than raise(3).
  */
 int genericRaise(int sig) {
-#if defined(THREADED_RTS) && (defined(openbsd_HOST_OS) || defined(freebsd_HOST_OS) || defined(dragonfly_HOST_OS) || defined(netbsd_HOST_OS))
+#if defined(THREADED_RTS) && (defined(openbsd_HOST_OS) || defined(freebsd_HOST_OS) || defined(dragonfly_HOST_OS) || defined(netbsd_HOST_OS) || defined(darwin_HOST_OS))
         return pthread_kill(pthread_self(), sig);
 #else
         return raise(sig);