[core] [api] Support OCaml 4.08

The changes are large due to `Pervasives` deprecation:

- the `Pervasives` module has been deprecated in favor of `Stdlib`, we
  have opted for introducing a few wrapping functions in `Util` and
  just unqualified the rest of occurrences. We avoid the shims as in
  the previous attempt.

- a bug regarding partial application have been fixed.

- some formatting functions have been deprecated, but previous
  versions don't include a replacement, thus the warning has been
  disabled.

We may want to clean up things a bit more, in particular
w.r.t. modules once we can move to OCaml 4.07 as the minimum required
version.

Note that there is a clash between 4.08.0 modules `Option` and `Int`
and Coq's ones. It is not clear if we should resolve that clash or
not, see PR #10469 for more discussion.

On the good side, OCaml 4.08.0 does provide a few interesting
functionalities, including nice new warnings useful for devs.

4 files changed, 17 insertions, 3 deletions

diff --git a/lib/future.ml b/lib/future.ml
index f6e9cee140..01fb7d0297 100644
--- a/lib/future.ml
+++ b/lib/future.ml
@@ -68,7 +68,7 @@ and 'a computation = 'a comput ref
 let unnamed = "unnamed"
 
 let create ?(name=unnamed) ?(uuid=UUID.fresh ()) f x =
-  ref (Ongoing (name, CEphemeron.create (uuid, f, Pervasives.ref x)))
+  ref (Ongoing (name, CEphemeron.create (uuid, f, ref x)))
 let get x =
   match !x with
   | Finished v -> unnamed, UUID.invalid, id, ref (Val v)
diff --git a/lib/pp.ml b/lib/pp.ml
index 542e5f6ecd..2f780677d9 100644
--- a/lib/pp.ml
+++ b/lib/pp.ml
@@ -197,9 +197,9 @@ let pp_with ft pp =
     | Ppcmd_print_break(m,n)  -> pp_print_break ft m n
     | Ppcmd_force_newline     -> pp_force_newline ft ()
     | Ppcmd_comment coms      -> List.iter (pr_com ft) coms
-    | Ppcmd_tag(tag, s)       -> pp_open_tag  ft tag;
+    | Ppcmd_tag(tag, s)       -> pp_open_tag  ft tag [@warning "-3"];
                                  pp_cmd s;
-                                 pp_close_tag ft ()
+                                 pp_close_tag ft () [@warning "-3"]
   in
   try pp_cmd pp
   with reraise ->
diff --git a/lib/util.ml b/lib/util.ml
index bac06b5701..61678f7669 100644
--- a/lib/util.ml
+++ b/lib/util.ml
@@ -8,6 +8,13 @@
 (*         *     (see LICENSE file for the text of the license)         *)
 (************************************************************************)
 
+type 'a pervasives_ref = 'a ref
+let pervasives_ref = ref
+let pervasives_compare = compare
+let (!) = (!)
+let (+) = (+)
+let (-) = (-)
+
 (* Mapping under pairs *)
 
 let on_fst f (a,b) = (f a,b)
diff --git a/lib/util.mli b/lib/util.mli
index 8ccb4b3f08..b6347126e0 100644
--- a/lib/util.mli
+++ b/lib/util.mli
@@ -8,6 +8,13 @@
 (*         *     (see LICENSE file for the text of the license)         *)
 (************************************************************************)
 
+type 'a pervasives_ref = 'a ref
+val pervasives_ref : 'a -> 'a ref
+val pervasives_compare : 'a -> 'a -> int
+val (!) : 'a ref -> 'a
+val (+) : int -> int -> int
+val (-) : int -> int -> int
+
 (** This module contains numerous utility functions on strings, lists,
    arrays, etc. *)