c++: fix count of z candidates for non-viable candidates, nesting [PR121966]

In r15-6116-gd3dd24acd74605 I updated print_z_candidates to show the
number of candidates, and a number for each candidate.

PR c++/121966 notes that the printed count is sometimes higher than
what's actually printed: I missed the case where candidates in the
list aren't printed due to not being viable.

Fixed thusly.

gcc/cp/ChangeLog:
	PR c++/121966
	* call.cc (print_z_candidates): Copy the filtering logic on viable
	candidates from the printing loop to the counting loop, so that
	num_candidates matches the number of iterations of the latter
	loop.

Signed-off-by: David Malcolm <[email protected]>

Author: davidmalcolm

gcc/cp/call.cc

@@ -4255,7 +4255,11 @@ print_z_candidates (location_t loc, struct z_candidate *candidates,
 
   int num_candidates = 0;
   for (auto iter = candidates; iter; iter = iter->next)
-    ++num_candidates;
+    {
+      if (only_viable_p.is_true () && iter->viable != 1)
+	break;
+      ++num_candidates;
+    }
 
   inform_n (loc,
 	    num_candidates, "there is %i candidate", "there are %i candidates",