PR#6501: harden the native-code generator against certain uses of "%identity".
Technically: when a C-- let-bound variable is assigned to, update its type
so that it is the lub of the types of the initial value and all values
assigned to it, with the type ordering Int <: Addr.


git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@15078 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02