New release of js_of_ocaml breaks picos.thread

[hhugo]

The new release of jsoo ocaml/opam-repository#26932 breaks picos.thread on ocaml < 5 because it no longer exports a caml_ml_domain_id runtime value on ocaml < 5.
I don't rely understand why picos is build with ocaml 4.

Is it ok to apply the following patch to thread.ocaml4.js ?

//Provides: caml_thread_self
//Requires: caml_ml_domain_id, caml_failwith, caml_thread
function caml_thread_self(unit) {
-   if (caml_ml_domain_id(unit) != caml_thread[1])
-    caml_failwith('caml_thread_self: spawning of domains is not supported')
  return caml_thread
}

[polytypic]

I don't rely understand why picos is build with ocaml 4.

Generally speaking Picos fully supports OCaml 4. One can use systhreads (i.e. the Thread module) in OCaml 4 and then run Picos fibers on systhreads. As long one doesn't use large numbers of fibers, it is entirely possible to write programs than can be built and run fine both with OCaml 4 and OCaml 5. The main intention behind this, of course, is to potentially help with porting applications to OCaml 5.

Is it ok to apply the following patch to thread.ocaml4.js ?

Hmm... Yes... I think we should also trim the Requires, but otherwise I think it should be fine.

Does #333 look good to you?

And thanks for opening the issue!

[hhugo]

Your PR looks good.