Follow removal of block in base.

Signed-off-by: Edward Z. Yang <ezyang@mit.edu>

smp/threads006/Main.hs

@@ -59,7 +59,7 @@ main :: IO ()
 main = do
     hSetBuffering stdout NoBuffering
     [nthreads] <- fmap (map read) getArgs
-    tids <- replicateM nthreads $ block $ forkIO $ return ()
+    tids <- replicateM nthreads . mask $ \_ -> forkIO $ return ()
     m <- newEmptyMVar
     -- do it in a subthread to avoid bound-thread overhead
     forkIO $ do mapM_ killThread tids; putMVar m ()