Improve handling of multiple S/R conflicts in the same state and of S/R

conflicts involving multiple reductions.
* src/conflicts.c (resolve_sr_conflict): Don't assign the error action
set for a state here or Bison will abort if it is reassigned on a
later conflicted reduction in the same state.
Similarly, don't finalize and assign the solved conflicts report here
or it will be lost if it is reassigned on a later conflicted reduction
in the same state.
(set_conflicts): Instead, assign them both here after all S/R conflicts
in the state have been fully examined.
* src/print.c (shift_set): Rename to...
(no_reduce_set): ... this.
(print_reductions): Update for rename, and add %nonassoc error action
tokens to no_reduce_set so that, when printing the first remaining
reduction on an error action token, the reduction is enclosed in
brackets.
(print_results): Update for rename.
* tests/conflicts.at (Solved conflicts report for multiple reductions
in a state): New test case.
(%nonassoc error actions for multiple reductions in a state): New test
case.

* src/main.c (main): Don't depend on C99 features.

src/main.c

@@ -116,11 +116,12 @@ main (int argc, char *argv[])
   timevar_push (TV_CONFLICTS);
   conflicts_solve ();
   {
-    state_number old_to_new[nstates];
+    state_number *old_to_new = xnmalloc (nstates, sizeof *old_to_new);
     state_number nstates_old = nstates;
     state_remove_unreachable_states (old_to_new);
     lalr_update_state_numbers (old_to_new, nstates_old);
     conflicts_update_state_numbers (old_to_new, nstates_old);
+    free (old_to_new);
   }
   conflicts_print ();
   timevar_pop (TV_CONFLICTS);