[m-rev.] for post-commit review: convert more passes to use var_tables

[Peter Wang]

On Sat, 30 Apr 2022 05:06:05 +1000 "Zoltan Somogyi" <zoltan.somogyi at runbox.com> wrote:
> Most of this is boring and does not need review, but I would like
> Peter to take a look at the new XXXs in tupling.m, in candidate_headvars_of_proc_2.
> Was the test that excluded unnamed variables from being put into tuples
> intentional, and if so, what was the reasoning behind it?

I don't remember (of course) but it should be related to this,
from the comment at the top of the file:

% Step 2 in more detail:
%
% This implementation uses the names of input formal parameters to guess
% which values are common between the procedures in an SCC (for SCCs with
% more than one procedure).

Unnamed vars can't be the input to any call, so I can't see how
it would be a missed opportunity.

Peter