Opam-free version check in Dynarray test

[jmid]

Fixes #503

By using ocaml-config:version from ocamlc -config instead of ocaml_version we should be able to get around having to generate a dune stanza... 🤞

(Note: only the first commit should be merged)

[jmid]

Well, that didn't work as dune still invokes ocamlopt on the modules on 5.0 and 5.1, e.g.:
https://github.com/ocaml-multicore/multicoretests/actions/runs/12631250102/job/35192635111?pr=504

(cd _build/default && /home/runner/local/bin/ocamlopt.opt -w @1..3@5..28@30..39@43@46..47@49..57@61..62-40 -strict-sequence -strict-formats -short-paths -keep-locs -g -I src/dynarray/.stm_tests.eobjs/byte -I src/dynarray/.stm_tests.eobjs/native -I /home/runner/local/lib/ocaml/unix -I lib/.STM.objs/byte -I lib/.STM.objs/native -I lib/.STM_domain.objs/byte -I lib/.STM_domain.objs/native -I lib/.STM_sequential.objs/byte -I lib/.STM_sequential.objs/native -I lib/.util.objs/byte -I lib/.util.objs/native -I qcheck/src/core/.qcheck_core.objs/byte -I qcheck/src/core/.qcheck_core.objs/native -I qcheck/src/runner/.qcheck_runner.objs/byte -I qcheck/src/runner/.qcheck_runner.objs/native -intf-suffix .ml -no-alias-deps -opaque -o src/dynarray/.stm_tests.eobjs/native/dune__exe__Stm_tests.cmx -c -impl src/dynarray/stm_tests.ml)
File "src/dynarray/stm_tests.ml", line 27, characters 18-28:
27 |   type sut = elem Dynarray.t list ref
                       ^^^^^^^^^^
Error: Unbound module Dynarray
Hint: Did you mean Bigarray?

65ecc42 thus attempts generating the dune rules dynamically.

[jmid]

Progress: Now it only scans stm_tests.ml and fails because of the missing QCheck dependency:
https://github.com/ocaml-multicore/multicoretests/actions/runs/12631841584/job/35194341447?pr=504

Run bash multicoretests/.github/runner.sh build
(cd _build/default && /home/runner/local/bin/ocamlopt.opt -w @1..3@5..28@30..39@43@46..47@49..57@61..62-40 -strict-sequence -strict-formats -short-paths -keep-locs -g -I src/dynarray/.stm_tests.eobjs/byte -I src/dynarray/.stm_tests.eobjs/native -intf-suffix .ml -no-alias-deps -opaque -open Dune__exe -o src/dynarray/.stm_tests.eobjs/native/dune__exe__Stm_tests.cmx -c -impl src/dynarray/stm_tests.ml)
File "src/dynarray/stm_tests.ml", line 1, characters 5-11:
1 | open QCheck
         ^^^^^^
Error: Unbound module QCheck
Error: Process completed with exit code 1.

53b5af6 thus switches to a generic (rule ...) without any .ml code dependencies.

[jmid]

The opam 4.12 installation workflow is failing - as ocaml_release was added in 4.14:
https://github.com/ocaml-multicore/multicoretests/actions/runs/12632373008/job/35195929875?pr=504

#=== ERROR while compiling qcheck-multicoretests-util.dev =====================#
# context     2.1.6 | linux/x86_64 | ocaml-base-compiler.4.12.1 | pinned(git+file:///home/runner/work/multicoretests/multicoretests#HEAD#e9d16510625d375f1d181f7da998477ce45ec082)
# path        ~/work/multicoretests/multicoretests/_opam/.opam-switch/build/qcheck-multicoretests-util.dev
# command     ~/.opam/opam-init/hooks/sandbox.sh build dune build -p qcheck-multicoretests-util -j 4 @install @runtest
# exit-code   1
# env-file    ~/.opam/log/qcheck-multicoretests-util-2346-6fc7e4.env
# output-file ~/.opam/log/qcheck-multicoretests-util-2346-6fc7e4.out
### output ###
# (cd src/dynarray && /home/runner/work/multicoretests/multicoretests/_opam/bin/ocaml -I +compiler-libs /home/runner/work/multicoretests/multicoretests/_opam/.opam-switch/build/qcheck-multicoretests-util.dev/_build/.dune/default/src/dynarray/dune.ml)
# File "src/dynarray/dune", line 6, characters 23-36:
# Error: Unbound value ocaml_release

d89d51a thus uses and parses Sys.ocaml_version instead... 🤞

[jmid]

CI summary: All 33 workflows passed. Merging.

[jmid]

CI summary for merge to main: All trunk workflows except MinGW bytecode trunk timed out #505

• 32bit trunk timed out after 240m in STM Sys test parallel
• Bytecode trunk timed out after 240m in STM Sys stress test parallel
• Cygwin trunk timed out after 240m in STM Sys stress test parallel
• FP trunk timed out after 240m in STM Sys stress test parallel
• Linux trunk timed out after 180m in STM Sys test parallel
• Linux trunk debug timed out after 240m in STM Sys test parallel
• MSVC bytecode trunk timed out after 240m in STM Sys stress test parallel
• MSVC trunk timed out after 180m in STM Sys test parallel
• MinGW trunk timed out after 240m in STM Sys stress test parallel
• macOS-ARM64 trunk timed out after 180m in STM Sys stress test parallel
• macOS-intel trunk timed out after 180m in STM Sys stress test parallel
• musl trunk timed out after 240m in STM Out_channel test parallel

Out of 34 workflows 12 timed out - with what appears to be a genuine regression.