add pragma

Author: bigfooted

Common/include/toolboxes/printing_toolbox.hpp

@@ -25,6 +25,8 @@
  * License along with SU2. If not, see <http://www.gnu.org/licenses/>.
  */
 
+#pragma once
+
 #include <iostream>
 #include <iomanip>
 #include <cstdint>