refactor: move findlib predicates (ocaml#8634)

Signed-off-by: Rudi Grinberg <me@rgrinberg.com>

src/dune_findlib/package0.mli

@@ -16,6 +16,7 @@ val ppx_runtime_deps : t -> Lib_name.t list
 val kind : t -> Lib_kind.t
 val archives : t -> Path.t list Mode.Dict.t
 val plugins : t -> Path.t list Mode.Dict.t
+val findlib_predicates_set_by_dune : Ocaml.Variant.Set.t
 
 module Exists
     (Monad : sig

src/dune_rules/findlib.ml

@@ -62,8 +62,6 @@ let hash { stdlib_dir; paths; builtins; ext_lib } =
     , String.hash ext_lib )
 ;;
 
-let findlib_predicates_set_by_dune = Ps.of_list [ P.ppx_driver; P.mt; P.mt_posix ]
-
 let has_double_underscore s =
   let len = String.length s in
   len >= 2

src/dune_rules/findlib.mli

@@ -5,8 +5,6 @@ open Import
 (** Findlib database *)
 type t
 
-val findlib_predicates_set_by_dune : Variant.Set.t
-
 module Unavailable_reason : sig
   type t =
     | Not_found

src/dune_rules/link_time_code_gen.ml

@@ -208,7 +208,7 @@ let findlib_predicates_set_by_dune pred =
    match Sys.backend_type, pred with
    | Sys.Native, "native" -> true
    | Sys.Bytecode, "byte" -> true|ocaml};
-  Variant.Set.iter Findlib.findlib_predicates_set_by_dune ~f:(fun variant ->
+  Variant.Set.iter Dune_findlib.Package.findlib_predicates_set_by_dune ~f:(fun variant ->
     pr buf "   | _, %S -> true" (Variant.to_string variant));
   pr buf "   | _, _ -> false";
   prlist buf "already_linked_libraries" (sorted_public_lib_names libs) ~f:(fun lib ->
@@ -253,7 +253,9 @@ let findlib_dynload cctx lib loc =
     ~name
     ~code:
       (Action_builder.delayed (fun () ->
-         findlib_init_code ~preds:Findlib.findlib_predicates_set_by_dune ~libs:all_libs))
+         findlib_init_code
+           ~preds:Dune_findlib.Package.findlib_predicates_set_by_dune
+           ~libs:all_libs))
     ~requires
     ~precompiled_cmi:false
 ;;