rustc and cargo are supported in buildroot. But even the latest buildroot master uses rust version 1.33.0 stable I think.
How can I use the a nightly version of rust in buildroot?
Update: This patch http://lists.busybox.net/pipermail/buildroot/2016-April/159523.html introduces rust in buildroot. And this buildroot repo https://github.com/elebihan/buildroot/tree/feature/rust-1.33.0 has some latest rustc version.