The old code used an array to store each "instruction group" (the new,
better name than the old overloaded "annotation"), and required a
memmove() to shift elements over in the array when we needed to split a
group so that we could add an error message. This was confusing and
difficult to get right, not the least of which was  because the array
has a tail sentinel not included in .ann_count.

Instead use a linked list, a data structure made for efficient
insertion.

Acked-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>