How to start developing?

I miss some functionality on this router, so I'd like to make my own programs. Just few simple C-program (for downloading or for collecting data from my-own-build anemometr). But I haven't found any suitable C (or C++) compiler for this platform. Is there any? Or how to develop cumstom aps?

Thanks for answering.

I've found gcc package for my router, so it solves my problem.