add your option in the project build option.
To do that, right clic in the workspace arrea on the name of your project (so you must use a project to generate your code).
Chhose Build Option... in the menu, you should see a window with your fortran compiler seeting (GNU fortran for me), select "Other options" at general level (or debug or relaease depending how your project is set), then add your option.
gd_on