1. With OCaml 3.11.0, if I write
ocamlc.opt -o myrun -make_runtime unix.cma
ocamlc.opt -o essai -use_runtime myrun unix.cma essai.ml
(with essai.ml:
let x = Unix.time() in
Format.printf "Here1 %f@." x;;)

and then ./essai

I get the following error message:

Fatal error: cannot load shared library dllunix
Reason: /usr/local/lib/ocaml/stublibs/dllunix.so: undefined symbol: 
caml_copy_int64

2. Until version 3.10.2, it was OK

3. I understandd that now, it is not necessary to use a custom runtime, 
as ocamlrun can load dynamically dllunix.so (in that case, ./essai works 
OK).

However, I would like that my Makefiles remain compatible with recent 
versions of OCaml.

Bertrand Jeannet