The cli is hidden-away in the BOINC-directory after installation, so you don't need to build it yourself. 😉
But, the easiest is to help beta-test v4.24, just remember to uninstall old version beforehand and choose to install v4.24 as service. 🙂
Uninstalling old BOINC-versinos will not lose your work, so it's not a problem.
Of course, you can also still use v4.19 and install as service, of so stop the gui, navigate to the BOINC-directyr and type
boinc_cli -install
If you're running XP, you very likely must go into the service-control-panel and choose to run the BOINC-service as "localsystem".
Start the service, or reboot. 😉