Gradle looks simple, but a Gradle build file is really a program in the Groovy programming language, so you can get all sorts of complicated with it. As an example, for my Android projects, I've got some Groovy code that calls out to Git to extract some version names and strings (based on the most recent git tag).

If you need output in some particular format, you can probably swing it. The real fun comes from all the plugins where somebody has already done the heavy lifting for you.

So you're building a teeny tiny JVM? Interesting. Sounds like you don't have much space for any sort of compiler on the platform. Have you thought about doing an ahead-of-time compiler, so all you're running on your tiny platform is native machine code + the runtime system?