The AVR/GNU archiver, avr-ar, combines a collection of object files into a single archive file, also known as a library.
Open the Project Properties on the menu Project → 'Your_project_name Properties'. This menu item is only available when a Static Library project is open. To configure Static Library options, click on the Toolchain property tab.
On the Toolchain property page, you will see AVR/GNU Archiver active and enabled. You may also see that the AVR/GNU Linker is disabled for a static library project.
You can set the AVR/GNU Archiver flags at the Archiver Flags textbox in the above General options.
Now, save the project and compile it by selecting Build Solution from the Build menu.