$ rustup target add x86_64-unknown-linux-musl
info: downloading component 'rust-std' for 'x86_64-unknown-linux-musl'
13.77 MiB / 13.77 MiB (100.00%) 1.47 MiB/s ETA: 0s
info: installing component 'rust-std' for 'x86_64-unknown-linux-musl'
$ cargo build --target x86_64-unknown-linux-musl
Though, I guess Android NDK uses a custom toolchain, linker, so it might not be that easily achieveable. Though it will give Rust an advantage over other newcomers. Crosscompilation for multiple OS'es/Architecture seems like a big selling point.
EDIT: Huh. I guess they do have binaries for arm linux now, at least for nightly and beta versions, as of literally two days ago.