message: Use dune lock to avoid racing access to cargo / rustup
diff: ; ocaml-gen
  (source_tree ../../ocaml-gen))
  (targets libocamlgen_test_stubs.a dllocamlgen_test_stubs.so)
  + (locks /cargo-lock)
  (action
  (progn
  (run rm -rf ./target)
  main.rs
  ; ocaml-gen
  (source_tree ../../ocaml-gen))
  + (locks /cargo-lock)
  (action
  (progn
  (run rm -rf ./target)
  