some minor changes:

- now that src/gdb uses automake, it requires the same hack that other
subdirectories that use automake require
- split off a copy of the top-level ChangeLog that just includes a list
of my own changes

(also if you are viewing this commit message via the ChangeLog file,
you should really be doing it from GitHub instead, as it has the actual
diffs and stuff)

Change-Id: Id4502e00ba2f82746e5c7c9de87e7a49fb582198