Cygwin: pty: Disable FreeConsole() on close for non cygwin process.

- After commit e1a0775dc0, the problem
  reported in https://www.cygwin.com/ml/cygwin/2020-01/msg00093.html
  occurs. For Gnu scren and tmux, calling FreeConsole() on pty close
  is necessary. However, if FreeConsole() is called, cygwin setup
  with '-h' option does not work. Therefore, the commit
  e1a0775dc0 delayed closing pty.
  This is the cause of the problem above. Now, instead of delaying
  pty close, FreeConsole() is not called if the process is non cygwin
  processes such as cygwin setup.

winsup/cygwin/fhandler_tty.cc

@@ -66,6 +66,7 @@ struct pipe_reply {
 static int pcon_attached_to = -1;
 static bool isHybrid;
 static bool do_not_reset_switch_to_pcon;
+static bool freeconsole_on_close = true;
 
 #if USE_API_HOOK
 static void
@@ -725,7 +726,8 @@ fhandler_pty_slave::~fhandler_pty_slave ()
       if (used == 0)
 	{
 	  init_console_handler (false);
-	  FreeConsole ();
+	  if (freeconsole_on_close)
+	    FreeConsole ();
 	}
     }
 }
@@ -2660,6 +2662,12 @@ fhandler_pty_slave::setup_locale (void)
 	}
 }
 
+void
+fhandler_pty_slave::set_freeconsole_on_close (bool val)
+{
+  freeconsole_on_close = val;
+}
+
 void
 fhandler_pty_slave::fixup_after_attach (bool native_maybe, int fd_set)
 {
@@ -2783,7 +2791,8 @@ fhandler_pty_slave::fixup_after_exec ()
       if (used == 1 /* About to close this tty */)
 	{
 	  init_console_handler (false);
-	  FreeConsole ();
+	  if (freeconsole_on_close)
+	    FreeConsole ();
 	}
     }