You can directly build the RiscV examples by running the following commands:

rustup target add riscv32im-unknown-none-elf
cargo build --release --examples

But that won't be very useful by itself. You probably want to execute and prove these examples. Have a look at test_elf.rs and the examples-builder for one way to run the examples from tests. Or see the end-to-end integration tests for how to run the examples as stand-alone ELF files.