How to solve "Thread.create: Resource temporarily unavailable" ?

Hi,

I was trying to see if elpi 1.18.2 could compile on s390x, using the
zelenka porterbox, but compilation fails with:
------------------------------------------------------------------
Log of the first failure: _log/dune+sepcomp1.log
------------------------------------------------------------------
executable: dune
args: exec tests/sources//sepcomp1.exe -- -I src/
Error: Thread.create: Resource temporarily unavailable
------------------------------------------------------------------
End log of the first failure: _log/dune+sepcomp1.log
------------------------------------------------------------------


and poking around reveals that other software have the same problem on
the platform, not on zelenka:
  https://github.com/ocaml-multicore/multicoretests/issues/374

To solve the issue one should push some max thread up to a more
reasonable value ; and the questions are:
- do that on the box side? on the test framework side?
- how?

Cheers,

J.Puydt

PS: I'm not subscribed to the list, so don't forget to CC me.