GDB 8.1 branching 2017-12-04 update

[Joel Brobecker]

> >> One thing that I was thinking it'd be nice to see about getting
> >> into 8.1 was the DWARF5 index stuff (standard replacement for 
> >> .gdb_index):
> >>
> >>  https://sourceware.org/ml/gdb-patches/2017-05/msg00577.html
[...]
> I've played around with that series for a few days (on and off...),
> and I've now pushed it in, with an important change that eliminates
> most of the risk, IMO -- the original series made GDB default
> to the new index format, while I left .gdb_index the default.
> This should allow users/distros experimenting, and hopefully
> any follow up fixes should be small/contained and easy to backport.

Makes sense indeed! Thanks for doing that, Pedro.

-- 
Joel