Use std::cout.flags(...)

As suggested by Ansgar in 41af1a2e

dune/solvers/solvers/cgsolver.cc

@@ -154,8 +154,8 @@ void CGSolver<MatrixType, VectorType>::solve()
                       << std::setw(9) << std::setprecision(5) << convRate
 
                       << std::endl;
-            std::cout << std::setprecision(oldPrecision)
-                      << std::setiosflags(oldFormatFlags);
+            std::cout << std::setprecision(oldPrecision);
+            std::cout.flags(oldFormatFlags);
         }
     }