[Dune] Install Dune on Mac Catalina

[Christian Engwer]

Dear Oswald,

could you please give us a bit more context, so that we can help you.

I seems to me that you are building an older version of dune.

If there are no strng reasons to stick to the old version, I suggest
you use the 2.7 release. If the problem then persists, it is best, if
you open a bug report in the issue tracker at
https://gitlab.dune-projet.org/. Please include a the logs in the bug
report, currently it is not clear where in the build process you
actually get this error.


Best
Christian