Using the vcs_to_changelog.py script

[Simon Marchi <simon.marchi@polymtl.ca>]

Hi binutils and gdb folks!

As you may or may not know, the glibc project has started using a script called
vcs_to_changelog.py to automatically generate their ChangeLogs.  They don't do
hand-written ChangeLog entries with their contributions.  Instead they generate
a ChangeLog file using that script when creating a release, passing it a range
of git commits for which to create ChangeLog entries.

I would very much like if we started using this in GDB, and it was suggested
that we could try to sync with binutils, as you might want to do the same.

Here's how it could work in practice:

1. We update our gnulib import to import the vcs_to_changelog.py script (it is
   distributed as a gnulib module).
2. We update src-release.sh to call the script and generate a single top-level
   ChangeLog that is included in the release tarball.

If we use the script as it is today, the ChangeLog generated for a binutils
release will contain entries for commits that don't concern binutils (for
example, that just touch a file under gdb/) and vice-versa.  I don't think
that's really a problem, since all the required information will be there,
there will just be additional information (which I doubt anybody will care
about).  But if really needed, I'm sure the script could be modified to filter
down the commits that touch only what's included in the binutils or GDB
release (I would prefer to avoid doing this unless absolutely necessary).

For illustrative purposes, here's what the script outputs for the last bunch
of commits in binutils-gdb:

  http://paste.ubuntu.com/p/x38zs82Rmt/

That's it, please let me know what you think.

Simon