Disable macos for now as it doesn't have ppoll

Next version I'll make a proper wrapper

Author: haesbaert

packages/iomux/iomux.0.1/opam

@@ -9,6 +9,7 @@ tags: ["io" "multiplexing" "poll" "ppoll" "epoll" "kevent" "kqueue"]
 homepage: "https://github.com/haesbaert/ocaml-iomux"
 doc: "https://haesbaert.github.io/ocaml-iomux"
 bug-reports: "https://github.com/haesbaert/ocaml-iomux/issues"
+available: os != "macos"
 depends: [
   "ocaml" {>= "4.08"}
   "dune" {>= "3.6"}