Reduce clutter due to extensions related ifdef code block generation and avoid changing many files when a new extension support is added with partial functionality. Reviewed-by: Aaron Ruby <aruby@blackberry.com> Acked-by: Yonggang Luo <luoyonggang@gmail.com> Acked-by: Adam Jackson <ajax@redhat.com> Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27246>