dwarf unwinder (only works on i386/x86_64) - now with eh_frame and debug_frame fallback

[Roland McGrath]

> Yes, I meant translation time. It would be wonderful if elfutils
> provides an easy way to, merge the tables, transform them to be
> "loadbase-relative" and generate a binary-search hdr for the result. I
> am not sure how urgent such an cleanup and optimization is, we don't
> have much experience with the user backtraces (or the kernel dwarf
> unwinder for that matter). It isn't on my "short-list" at the moment.

It's certainly on the "in the fullness of time" list for elfutils. :-)