pkg: OpenBSD tar still lacks -z in 3.22.0_alpha2

[mndrix]

Expected Behavior

Previously described in #13688 by @Alizter

Actual Behavior

...
Shared cache enabled cache_enabled: Enabled
Shared cache location root_dir: "/home/michael/.cache/dune/db"
Workspace root root: "/home/michael/conf/ocaml"
Auto-detected concurrency concurrency: 1
Dune context context: { name = "default"
; kind = lock { default = true }
; profile = Dev
; merlin = true
; fdo_target_exe = None
; build_dir = In_build_dir "default"
; instrument_with = []
}
Toolchains cache location dir: "/home/michael/.cache/dune/toolchains"
Running[5]: /home/michael/.local/bin/curl -L -s --user-agent dune.3.22.0_alpha2 --write-out '"%{http_code}"' -o _build/.temp/dune_98367d_ocaml-5.4.1.tar.gz/download --compressed -- https://github.com/ocaml/ocaml/releases/download/5.4.1/ocaml-5.4.1.tar.gz > /tmp/dune_db436d_output 2> _build/.temp/dune_98367d_ocaml-5.4.1.tar.gz/curl.stderr
tar: unknown option -- -
usage: tar {crtux}[014578beFfHhjLmNOoPpqsvwXZz]
           [blocking-factor | format | archive | replstr]
           [-C directory] [-I file] [file ...]
       tar {-crtux} [-014578eHhjLmNOoPpqvwXZz] [-b blocking-factor]
           [-C directory] [-F format] [-f archive] [-I file]
           [-s replstr] [file ...]
File "dune.lock/ocaml-compiler.5.4.1.pkg", line 407, characters 3-76:
407 |    https://github.com/ocaml/ocaml/releases/download/5.4.1/ocaml-5.4.1.tar.gz)
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Error: failed to extract 'download'
Reason: 'tar' failed with non-zero exit code '1' and output:
- tar: input compressed with gzip; use the -z option to decompress it

In past versions of this bug, I don't remember seeing tar: unknown option -- - followed by the usage message, so maybe the tar flags are being constructed incorrectly now?

Reproduction

dune build on OpenBSD with dune version 3.22.0_alpha2 and a package dependency with a .tar.gz tarball.

Specifications

• Version of dune (output of dune --version): 3.22.0_alpha2
• Version of ocaml (output of ocamlc --version): 5.4.1
• Operating system (distribution and version): OpenBSD 7.8 amd64

Additional information

• Link to gist with verbose output (run dune with the --verbose flag):

[Alizter]

Can you attach the output of dune trace cat, or just the last few lines. I would like to see the exact commands that are being invoked here.

[mndrix]

Can you attach the output of dune trace cat

Certainly: dune-trace-cat.log

[Alizter]

We are calling --version to probe the tar implementation but this fails so we default to not passing -z. The fix here is to make the probe for the implementation more robust.

[Alizter]

I've opened #13825 since this actually is the symptom of another bug. We should be falling back to the Other tar implementation which is correct for OpenBSD however the reason we are not passing -z is because we are incorrectly detecting the file type.