[compiler] Fix data race in JSObject::RawFastInobjectPropertyAtPut

Mark the write of the property as relaxed atomic. The compiler thread
is examining the value. It is fine if the value is stale or new, we
simply need to let TSAN know we are aware of the race.

BUG=v8:11896

Change-Id: I42505a6e12c7eb3c1ef8d9376d7a420567646d62
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2968403Reviewed-by: Santiago Aboy Solanes <solanes@chromium.org>
Commit-Queue: Michael Stanton <mvstanton@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75209}

src/objects/js-objects-inl.h

@@ -384,7 +384,7 @@ void JSObject::RawFastInobjectPropertyAtPut(FieldIndex index, Object value,
                                             WriteBarrierMode mode) {
   DCHECK(index.is_inobject());
   int offset = index.offset();
-  WRITE_FIELD(*this, offset, value);
+  RELAXED_WRITE_FIELD(*this, offset, value);
   CONDITIONAL_WRITE_BARRIER(*this, offset, value, mode);
 }