Do not fail when "ocamlbuild -clean" fails
Do not fail when "ocamlbuild -clean" fails

It fails in some situations (such as NFS) and with some versions.

See: https://github.com/ocaml/ocamlbuild/issues/146

glondu/belenios,glondu/belenios,glondu/belenios,glondu/belenios,glondu/belenios