Before unwinding the stack, __asan_handle_no_return is supposed to
unpoison the entire stack - that is, remove the entries in the shadow
memory corresponding to stack (e.g. redzone markers around variables).
This does not work correctly if __asan_handle_no_return is called from
the alternate stack used in signal handlers, because the stack top is
read from a cache, which yields the default stack top instead of the
signal alternate stack top.
It is also possible to jump between the default stack and the signal
alternate stack. Therefore, __asan_handle_no_return needs to unpoison