GDB 8.3 release update (2019-03-25)

[Eli Zaretskii]

> Date: Mon, 25 Mar 2019 13:43:07 -0700
> From: Joel Brobecker <brobecker@adacore.com>
> 
> If we can confirm there aren't any issues we know of that we want
> to fix for 8.3, I could create the release, say, this weekend, or
> early next week.

All the problems I knew about are fixed, but I wonder whether we need
another pretest, since so many non-trivial changes went in.