with-dkml is not re-entrant

[jonahbeckford]

During opam install, where opam.exe is a with-dkml.exe shim, opam can call ocaml (ex. ocaml gen_config_ml in the ocaml-system package).

But that ocaml is another with-dkml.exe shim, and prints the following during DKML_BUILD_TRACE=ON opam init ...:

ocamlc: [INFO] Running command: /usr/bin/env
                                  /Users/jonah/Applications/DkMLNative/bin/ocamlc-real
                                  -vnum
4.14.0

That unexpected output messes up the ocaml-system package, and will mess up other packages in hard-to-understand ways.