conf-openblas: fix installation on Rocky9

[edwintorok]

opam var says:

os                linux              # Inferred from system
os-distribution   rocky              # Inferred from system
os-family         rhel               # Inferred from system
os-version        9.6                # Inferred from system

Rocky needs similar flags to centos, use os-family to cover other RHEL compatible distros.

Tested that I can now install owl on Rocky9.

[edwintorok]

(although TBH it might be better if all of these used pkg-config, but I don't want to break other distros, so I've done just the minimal change to get it working on Rocky)

[jmid]

LGTM, thanks!

IIUC, compared to conf-openblas.0.2.2/opam there are rhel cases added in the first and last build lines and in the second (centos) depexts case.

Extra thanks for sharing os, os-distribution and os-family values! 🙏
I think it would be a good idea to add these to https://github.com/ocaml/opam-repository/wiki/Depexts-os-distribution---os-family-values but I don't have permission to do so myself.
(While we are at it, we should also add an os column to the first table for consistency)

[jmid]

I've now opened #28930 to keep track of the os-triple and to unblock this PR from getting merged.

[mseri]

Thanks. I see that brew openblas is broken again on macos :( but it is no fault of anybody here