ocamlmklib: use ar rcs instead of ar rc (#11670)

Under macOS at least, `ar rc` on an empty list of files produces an archive
with no table of contents, which triggers an error when linked.

With `ar rcs`, we force the creation of a table of contents.  macOS prints
a warning, but the resulting archive causes no errors during linking.

The `s` option to `ar` is specified as "an XSI extension" in
IEEE Std 1003.1-2017, but seems supported by all the toolchains we care about.

The call to `ar rc` in utils/ccomp.ml is unchanged because the list
of object files is never empty, and IEEE Std 1003.1 says that `ar rc`
must create a symbol table in this case.

Follow-up to #11184

(cherry picked from commit 2f0c77c)

Changes

@@ -1,6 +1,11 @@
 OCaml 4.14 maintenance branch
 -----------------------------
 
+### Compiler user-interface and warnings:
+
+- #11184, #11670: Stop calling ranlib on created / installed libraries
+  (Sébastien Hinderer and Xavier Leroy, review by the same)
+
 ### Build system:
 
 - #11370, #11373: Don't pass CFLAGS to flexlink during configure.

tools/ocamlmklib.ml

@@ -26,7 +26,7 @@ let mklib out files opts =
     else ""
   in
   Printf.sprintf "link -lib -nologo %s-out:%s %s %s" machine out opts files
-  else Printf.sprintf "%s rc %s %s %s" Config.ar out opts files
+  else Printf.sprintf "%s rcs %s %s %s" Config.ar out opts files
 
 (* PR#4783: under Windows, don't use absolute paths because we do
    not know where the binary distribution will be installed. *)