testsuite: Add T5611a

This is the same as T5611 but with an unsafe call to sleep.

testsuite/tests/concurrent/should_run/T5611a.hs

+-- The same as T5611 but with unsafe calls.
+
+{-# LANGUAGE CPP,ForeignFunctionInterface #-}
+
+import Control.Concurrent
+import Foreign.C
+import System.IO
+
+#if defined(mingw32_HOST_OS)
+sleep n = sleepBlock (n*1000)
+foreign import stdcall unsafe "Sleep" sleepBlock :: Int -> IO ()
+#else
+sleep n = sleepBlock n
+foreign import ccall unsafe "sleep" sleepBlock :: Int -> IO ()
+#endif
+
+main :: IO ()
+main = do
+     hSetBuffering stdout LineBuffering
+
+     tid <- forkIO $ do
+         putStrLn "child: Sleeping"
+         _ <- sleep 1
+
+         -- The following lines should not happen after the killThread from the
+         -- parent thread completes.  However, they do...
+         -- putStrLn "child: Done sleeping"
+         threadDelay 100000
+         putStrLn "child: Done waiting"
+
+     threadDelay 100000
+     -- putStrLn $ "parent: Throwing exception to thread " ++ show tid
+     throwTo tid $ userError "Exception delivered successfully"
+     putStrLn "parent: Done throwing exception"
+
+     threadDelay 200000

testsuite/tests/concurrent/should_run/T5611a.stderr

+T5611a: user error (Exception delivered successfully)

testsuite/tests/concurrent/should_run/T5611a.stderr.mingw32

+T5611a: <stdout>: commitBuffer: user error (Exception delivered successfully)

testsuite/tests/concurrent/should_run/T5611a.stdout

+child: Sleeping
+parent: Done throwing exception

testsuite/tests/concurrent/should_run/all.T

@@ -74,10 +74,8 @@ test('T5558',
      compile_and_run, [''])
 
 test('T5421', normal, compile_and_run, [''])
-test('T5611',
-     [expect_broken_for(16845, ['ghci']),
-      when(opsys('darwin'), fragile(12751))],
-     compile_and_run, [''])
+test('T5611', when(opsys('darwin'), fragile(12751)) , compile_and_run, [''])
+test('T5611a', when(opsys('darwin'), fragile(12751)) , compile_and_run, [''])
 test('T5238', normal, compile_and_run, [''])
 test('T5866', exit_code(1), compile_and_run, [''])