ocaml-modules.ssl: make openssl propagatedBuildInput

pkgs/development/ocaml-modules/ssl/default.nix

···
     sha256 = "0i0j89b10n3xmmawcq4qfwa42133pddw4x5nysmsnpd15srv5gp9";
   };
 
-  buildInputs = [which openssl ocaml findlib];
+  buildInputs = [which ocaml findlib];
+
+  propagatedBuildInputs = [openssl];
 
   dontAddPrefix = true;