Include iostream in benchmark

python/dune/perftool/sumfact/autotune.py

@@ -74,6 +74,7 @@ def generate_standalone_code(sf, filename, logname):
                       "#include<dune/perftool/sumfact/horizontaladd.hh>\n",
                       "#include<random>\n",
                       "#include<fstream>\n",
+                      "#include<iostream>\n",
                       "\n"
                       ])