fix(pkg): handle empty ID_LIKE (ocaml#11726)

On NixOS for whatever reason `ID_LIKE` was an empty string. In this case
we shouldn't use it to find the `os_family` and instead fallback to the
`os_distribution`.

Signed-off-by: Ali Caglayan <[email protected]>

Author: Alizter

src/dune_pkg/sys_poll.ml

@@ -195,6 +195,7 @@ let os_family ~os_distribution ~os_release_fields ~os =
   | Some "linux" ->
     (match List.assoc (Lazy.force os_release_fields) "ID_LIKE" with
      | None -> os_distribution
+     | Some "" -> os_distribution
      | Some s ->
        (* first word *)
        (match Scanf.sscanf s " %s" Fun.id with