Converts an OCaml number to a canonical integer literal of type :int.
DESCRIPTION
The call mk_intconst n where n is an OCaml number (type num) produces
the canonical integer literal of type :int representing the integer n. This
will be of the form `&m' for a numeral m (when n is nonnegative) or
`-- &m' for a nonzero numeral m (when n is negative).
FAILURE CONDITIONS
Fails if applied to a number that is not an integer (type num also includes
rational numbers).
EXAMPLE
# mk_intconst (Int (-101));;
val it : term = `-- &101`
# type_of it;;
val it : hol_type = `:int`