A program can use `make-arity-wrapper-procedure` to synthesize a
function that reports a given arity mask (without calling `compile`).
In addition, `set-arity-wrapper-procedure!` suports modifying the
implementation of a synthesized procedure. Although similar
functionality could be achieved with `(lambda args (apply (unbox proc)
args))`, an arity wrapper procedure can dispatch to another procedure
without allocating a list for the arguments.
The interpreter now uses an internal variant of arity wrappers to
cooperate with `procedure-arity-mask`.
original commit: 295255a326afbf3f120f95c2ccc6e95b74fdd5e2
