* exceptions.cc (signal_exit): Reset all mutos owned by the main thread.

* fhandler.h: Define *_output_mutex macros for serializing tty output.
(fhandler_termios): Remove restart_output_event.  Define dummy output mutex
methods.
(fhandler_pty_master): Remove unneeded fixup_after_fork method.
* fhandler_termios.cc (fhandler_termios::line_edit): Acquire output_mutex when
CTRL-S is hit.  Release it on CTRL-Q.
* fhandler_tty.cc (fhandler_pty_master::process_slave_output): Remove
inappropriate OutputStopped test here.  Just use the output mutex.
(fhandler_pty_master::fhandler_pty_master): Remove obsolete reference to
restart_output_event.
(fhandler_tty_common::close): Ditto.
(fhandler_pty_master::set_close_on_exec): Ditto.
(fhandler_pty_master::fixup_after_fork): Delete.
* tty.cc (tty::common_init): Ditto.
* sync.cc (muto::reset): New method.
* sync.h: Declare above method.

winsup/cygwin/sync.cc

@@ -125,3 +125,16 @@ muto::release ()
 
   return 1;	/* success. */
 }
+
+/* Call only when we're exiting.  This is not thread safe. */
+void
+muto::reset ()
+{
+  visits = sync = tid = 0;
+  InterlockedExchange (&waiters, -1);
+  if (bruteforce)
+    {
+      CloseHandle (bruteforce);
+      bruteforce = CreateEvent (&sec_none_nih, FALSE, FALSE, name);
+    }
+}