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

[Julien Fischer]

On Tue, 11 Jul 2023, Julien Fischer wrote:

> A bootcheck with the 64-bit version of MSVC in hlc.gc with the updated
> GC succeeds without issue. (I was using the NO_MSGBOX_ON_ERROR fix, but
> that shouldn't matter.) I'll do a bootcheck with 32-bit MSVC
> (and DONT_USE_USER32_DLL) this evening.

The bootcheck with 32-bit MSVC was also successful.

Julien.