[m-rev.] for review: update to Boehm GC v8.0.6

[Julien Fischer]

Hi Peter,

The subject says you are updating to version 8.0.6 but the log message
says version 8.2.0.  Which is it?

On Mon, 29 Nov 2021, Peter Wang wrote:

> I'd like to update Boehm GC at this time, and libatomic_ops with it.
> I've pushed changes to our repos:
>
> libatomic_ops
>    updated branch: release-7_6-mercury
>    new tag: release-7_6-mercury-20211129
>
> bdwgc
>    new branch: release-8_0-mercury
>    new tag: release-8_0-mercury-20211129
>
> The following diff updates the Mercury repository. I haven't applied it.
>
> The bdwgc v8.0.x branch can make use gcc/clang atomic intrinsics instead
> of libatomic_ops. Unfortunately, we would still need to keep
> libatomic_ops around for MSVC.

Recent versions of MSVC, might provide the necessary intrinsics but I
guess Boehm doesn't use them yet?

> We should be able to enable munmap support by default once the upgrade
> is done.

No objection from me.  Has the upgrade been tested much?

Cheers,
Julien.