Const for runtime constraint

It allows to have non-standard limits for non-standard runtime.
ie: js_of_ocaml use 32bits integer, and can handle
string much bigger than 16Mo.
On Sat, 27 Sep 2014 15:08:41 -0700, hhugo wrote:
> 
> In stdlib/sys.mli:
> 
> > @@ -99,6 +99,9 @@ val word_size : int
> >  (** Size of one word on the machine currently executing the OCaml
> >     program, in bits: 32 or 64. *)
> >
> > +val int_size : int
> > +(** Size of one int, in bits: 31 or 63. *)
> 
> True, the point is to make this 32 when compiling to JavaScript.
> This comment is true for (apply to) the runtime distributed with the OCaml
> compiler.
> Would you prefer the following comment ?
> 
> (** Size of one int, usually 31 or 63 bits. *)

Why not be more specific?  What about something like:

(** Size of an int.  It is 31 bits (resp. 63 bits) when using the
    OCaml compilers on a 32 bits (resp. 64 bits) platform.  It may
    differ for other compilers, e.g. it is 32 when compiling to
    JavaScript. *)