[ocaml5-issue] Abort on domain_joingraph under debug runtime

[jmid]

For the merge of #400 to main the tests triggered an abort on domain_joingraph under Linux trunk/5.2 with the debug runtime:
https://github.com/ocaml-multicore/multicoretests/actions/runs/6479810327/job/17594078868

random seed: 71836890
generated error fail pass / total     time test name

[ ]    0    0    0    0 /  100     0.0s Domain.spawn/join - tak work
[ ]    0    0    0    0 /  100     0.0s Domain.spawn/join - tak work (generating)
[✓]  100    0    0  100 /  100    35.0s Domain.spawn/join - tak work

[03] file runtime/domain.c; line 1035 ### Assertion failed: di->backup_thread_msg == BT_INIT || di->backup_thread_msg == BT_TERMINATE
File "src/domain/dune", line 6, characters 7-23:
6 |  (name domain_joingraph)
           ^^^^^^^^^^^^^^^^
(cd _build/default/src/domain && ./domain_joingraph.exe --verbose)
Command got signal ABRT.
[ ]    0    0    0    0 /  500     0.0s Domain.spawn/join - atomic

The symptoms are similar to those reported in ocaml/ocaml#11800 and #386 so it may be caused by the same underlying runtime bug. I'm wondering whether it is a coincidence this is observed only at start-up during the very first test iteration both here and in #386... 🤔

[jmid]

Fixed in ocaml/ocaml#12707