[m-rev.] for review: update to Boehm GC v8.2.4

[Julien Fischer]

Hi Peter,

On Mon, 10 Jul 2023, Peter Wang wrote:

> Hi Julien,
>
> I've pushed the tag 'release-8_2-mercury-20230706-rc' to our
> bdwgc repository. Can you test it on MacOS and Windows?

I assume I just checkout that tag in the boehm_gc directory of
my workspace?  Do I need to do anything with libatomic_ops?

Julien.