message: fix build failure with clang trunk
diff: @@ -276,7 +276,7 @@ void CFG::printDot(ostream &os) const {
  os << "digraph {\n"
  "\"" << bb_dot_name(f.getBBs()[0]->getName()) << "\" [shape=box];\n";
  - for (const auto &[src, dst, instr] : *this) {
  + for (auto [src, dst, instr] : *this) {
  (void)instr;
  os << '"' << bb_dot_name(src.getName()) << "\" -> \""
  << bb_dot_name(dst.getName()) << "\";\n";
  