As for exit, also allows concurrent quick_exit to avoid race
conditions when it is called concurrently. Since it uses the same
internal function as exit, the __exit_lock lock is moved to
__run_exit_handlers. It also solved a potential concurrent when
calling exit and quick_exit concurrently.
The test case 'expected' is expanded to a value larger than the
minimum required by C/POSIX (32 entries) so at_quick_exit() will
require libc to allocate a new block. This makes the test mre likely to
trigger concurrent issues (through free() at __run_exit_handlers)
if quick_exit() interacts with the at_quick_exit list concurrently.
This is also the latest interpretation of the Austin Ticket [1].
Checked on x86_64-linux-gnu.
[1] https://austingroupbugs.net/view.php?id=1845
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
