Bug#18235: assertion/crash when windows mysqld is ended with ctrl-c

Two threads both try a shutdown sequence which creates a race to the
de-init/free of certain resources.

This exists in similar form in the client as 17926: "mysql.exe crashes
when ctrl-c is pressed in windows."

sql/mysqld.cc

@@ -991,7 +991,11 @@ static void __cdecl kill_server(int sig_ptr)
   my_thread_init();				// If this is a new thread
 #endif
   close_connections();
-  if (sig != MYSQL_KILL_SIGNAL && sig != 0)
+  if (sig != MYSQL_KILL_SIGNAL &&
+#ifdef __WIN__
+      sig != SIGINT &&				/* Bug#18235 */
+#endif
+      sig != 0)
     unireg_abort(1);				/* purecov: inspected */
   else
     unireg_end();