Have you explored Bazel? It's a fast, scalable, and language-agnostic build system developed by Google. The open source version is technically labelled as beta, but it's based on the system that Google uses in production.
Hmm, I might have skipped that one because it's Java and I thought I'd need a JVM. But I might have been wrong, the setup guide does not mention it. (EDIT: It does mention JDK in the FAQ)
I did look into language-agnostic ones, but since SCons was just "okay", not a whole lot more. I should probably check Bazel out some more, if only to save a lot of effort starting from scratch.