Fix waitForProcess not closing the handle when raising delegated Ctrl-C

endDelegateControlC throws UserInterrupt, which would cause
modifyProcessHandle to roll back, leaving the handle open
despite the waitpid call.

Instead, we postpone the call to endDelegateControlC, as is already
the case in getProcessExitCode.

Additionally, remove endDelegateControlC entirely from the Windows-only
OpenExtHandle branch, where it's a no-op and was also in the wrong place.

Author: robx

System/Process.hs

@@ -703,15 +703,15 @@ waitForProcess ph@(ProcessHandle _ delegating_ctlc _) = lockWaitpid $ do
     OpenHandle h  -> do
         -- don't hold the MVar while we call c_waitForProcess...
         e <- waitForProcess' h
-        e' <- modifyProcessHandle ph $ \p_' ->
+        (e', was_open) <- modifyProcessHandle ph $ \p_' ->
           case p_' of
-            ClosedHandle e' -> return (p_', e')
+            ClosedHandle e' -> return (p_', (e', False))
             OpenExtHandle{} -> fail "waitForProcess(OpenExtHandle): this cannot happen"
             OpenHandle ph'  -> do
               closePHANDLE ph'
-              when delegating_ctlc $
-                endDelegateControlC e
-              return (ClosedHandle e, e)
+              return (ClosedHandle e, (e, True))
+        when (was_open && delegating_ctlc) $
+          endDelegateControlC e
         return e'
 #if defined(WINDOWS)
     OpenExtHandle h job -> do
@@ -725,8 +725,6 @@ waitForProcess ph@(ProcessHandle _ delegating_ctlc _) = lockWaitpid $ do
             OpenExtHandle ph' job' -> do
               closePHANDLE ph'
               closePHANDLE job'
-              when delegating_ctlc $
-                endDelegateControlC e
               return (ClosedHandle e, e)
         return e'
 #else