When handling function calls, we often want to walk through the list of
formal parameters and list of actual parameters at the same time.
(Both are guaranteed to be the same length.)

Previously, we used a pattern of:

   exec_list_iterator 1st_iter = <1st list>.iterator();
   foreach_iter(exec_list_iterator, 2nd_iter, <2nd list>) {
      ...
      1st_iter.next();
   }

This was awkward, since you had to manually iterate through one of
the two lists.

This patch introduces a foreach_two_lists macro which safely walks
through two lists at the same time, so you can simply do:

   foreach_two_lists(1st_node, <1st list>, 2nd_node, <2nd list>) {
      ...
   }

v2: Rename macro from foreach_list2 to foreach_two_lists, as suggested
    by Ian Romanick.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>