[m-rev.] Upgrade Boehm GC to 7.6.0

[Julien Fischer]

On Wed, 21 Sep 2016, Paul Bone wrote:

>>> The best I could do last time was to commit the files that libtool
>>> generates, so that it's not needed during normal builds.  I'm currently
>>> setting up an environment similar to Zoltan's without libtool so that I can
>>> see more of what is happening.  Maybe my change didn't go through when
>>> Zoltan did his testing or maybe I screwed up, not sure.
>>
>> I just "fixed" the problem another way, by taking ltmain.sh and the
>> contents of the m4 directory from the libatomic_ops-7.4.4 tarball (from
>> the Boehm GC webapage) and copying them into my source tree.  It then
>> works.  (In the git version ltmain.sh is currently a symlink to
>> somewhere that doesn't exist on my system.)  I think it might be best if
>> we just commit the above files in the Mercury version of libatomic_ops.
>
> Agreed,
>
> I can do that.

That would have the additional benefit of getting rid of all the
symlinks that are currently there.

Julien.