dune build warning with ocaml 5.0

[fblanqui]

14:13 ~/lambdapi (indexing) dune build
File "_none_", line 1:                 
Alert ocaml_deprecated_auto_include: 
OCaml's lib directory layout changed in 5.0. The unix subdirectory has been
automatically added to the search path, but you should add -I +unix to the
command-line to silence this alert (e.g. by adding unix to the list of
libraries in your dune file, or adding use_unix to your _tags file for
ocamlbuild, or using -package unix for ocamlfind).

[fblanqui]

Fixed in #1022

[fblanqui]

duplicate of #968 not specific to ocaml 5.0