message: Make SingleImpl warning quieter
  Summary: Print a single warning to re-run with tracing.
diff: @@ -294,7 +294,14 @@ void AnalysisImpl::escape_cross_stores() {
  if (cls != nullptr) {
  if (xstores.illegal_ref_load_types(intf_it.first, cls)) {
  escape_interface(intf_it.first, CROSS_STORES);
  + static bool warned = false;
  + if (!warned) {
  + warned = true;
  TRACE(INTF, 0,
  + "Found transitive cross store violation! For details, run with "
  + "TRACE=INTF:1.");
  + }
  + TRACE(INTF, 1,
  "Warning: found %s which is by itself not a cross-store "
  "violation for %s but depends on other types that are!",
  SHOW(cls), SHOW(intf_it.first));
  