pan/bi: Use a dynarray for predecessors

pan/bi: Use a dynarray for predecessors

This is deterministic, unlike a set. Note we need the extra dereferencing to
keep the macro safe, simple, and standards compliant:

1. Nesting two for-loops would cause break/continue to fail.
2. Declaring variables outside the loop would pollute the namespace.
3. Declaring an anonymous struct is not conformant and doesn't compile in clang.

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16279>