Array read operations are missing a read barrier

It turns out that pointer-array reads are currently missing the necessary acquire barrier to ensure soundness on platforms with weak memory ordering.

added Phighest RTS Tbug backport needed:9.2 backport needed:9.4 backport needed:9.6 concurrency labels

assigned to @bgamari

mentioned in commit c4e038ab

removed backport needed:9.2 label

mentioned in commit ff9624a4

mentioned in commit c32e4e2e

mentioned in commit 72841699

mentioned in commit 9a3d7cdd

mentioned in merge request !10953 (closed)

mentioned in commit e54ae5d6

mentioned in commit 9cc6693b

mentioned in commit a93de317

mentioned in commit 01373f0e