[rfa] add 'parent' field to struct die_info

[Jim Blandy]

Elena Zannoni <ezannoni@redhat.com> writes:
> Each debugging information entry is defined either to have child
> entries or not to have child entries. If an entry is defined not to
> have children, the next physically succeeding entry is a sibling. If
> an entry is defined to have children, the next physically succeeding
> entry is its first child. Additional children are represented as
> siblings of the first child. A chain of sibling entries is terminated
> by a null entry.

Sure, that sort of explanation would be appropriate for the die
reading code, but I think it would just be confusing for 'struct
die_info'.  Once we've built the die tree in memory, all that detail
is gone, and you've just got the pure tree structure.  There's no
concept of "the next physically succeeding entry", for example.