[m-rev.] diff: Update to Boehm GC v8.2.4 and libatomic_ops v7.8.0

[Peter Wang]

Remember to run "git submodule update --recursive" to bring
the submodules in your workspace up to date.

--- 

.gitmodules:
boehm_gc:
    Update boehm_gc submodule to release-8_2-mercury-20230712.

NEWS.md:
    Announce change.
---
 .gitmodules | 2 +-
 NEWS.md     | 5 +++++
 boehm_gc    | 2 +-
 3 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/.gitmodules b/.gitmodules
index ce44269cd..eff4f58b0 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -1,5 +1,5 @@
 [submodule "boehm_gc"]
 	path = boehm_gc
 	url = ../bdwgc.git
-	branch = release-8_0-mercury
+	branch = release-8_2-mercury
 	update = checkout
diff --git a/NEWS.md b/NEWS.md
index 3e43d21ba..38b9f0903 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1199,6 +1199,11 @@ Changes to the Mercury debugger
 * The `dump` command has a new option: `dump -p Var` will dump the value
   of the given variable in a prettyprinted form.
 
+Changes to the Mercury implementation
+-------------------------------------
+
+* We have upgraded the bundled Boehm GC to v8.2.4 and libatomic_ops to v7.8.0.
+
 Portability improvements
 ------------------------
 
diff --git a/boehm_gc b/boehm_gc
index 84e76dd6f..90d9234e5 160000
--- a/boehm_gc
+++ b/boehm_gc
@@ -1 +1 @@
-Subproject commit 84e76dd6ff00266065020ee1cfb4f9eaba87a84d
+Subproject commit 90d9234e52155de119e906da950086ed2a588670
-- 
2.39.0