replace std::quick_exit with std::_Exit

std::quick_exit is not supported on every platform
https://stackoverflow.com/questions/11681403/state-of-c11-standard-support-in-libc/60496235#60496235

One could check for _GLIBCXX_HAVE_QUICK_EXIT/_LIBCPP_HAS_QUICK_EXIT
and switch to std::exit, but std::_Exit should work on every platform
and have the same effect as std::quick_exit (assuming at_quick_exit is
not used).