Use c++ standard std::_Exit instead of _exit

_exit seems to run dll unloading code which calls static destructors.
Standrd requires std::_Exit not to call destructors which makes using it
attractive in case MSVC actually follows the standard.

library/Core.cpp

@@ -1163,7 +1163,7 @@ command_result Core::runCommand(color_ostream &con, const std::string &first_, v
         }
         else if (builtin == "die")
         {
-            _exit(666);
+            std::_Exit(666);
         }
         else if (builtin == "kill-lua")
         {