My advice is for the OP to make his build system GPLv3 licensed and sue anyone who willfully violates that license.

Open source still has lots of life left in it, but copyleft licenses are now increasing in importance, and the days of letting it slide when a company violates your license are now gone.

To decide on what license you want, ask yourself, do you want this to improve software as a whole, or do you want this to improve FOSS? Does the image of proprietary software benefiting from your work soothe or anger you? Nowadays, it's becoming increasingly important to choose the latter. If you don't care what happens, you can license it as MIT or something. There are still valid cases for that.