ocaml-option-fp only available on linux x86_64

Author: dra27

packages/ocaml-option-fp/ocaml-option-fp.1/opam

@@ -4,5 +4,6 @@ depends: [
   "ocaml-variants" {post & >= "4.12.0~"}
 ]
 conflicts: ["ocaml-option-musl"]
+available: os = "linux" & arch = "x86_64"
 maintainer: "[email protected]"
 flags: compiler