Install toolchain:
rustup target add thumbv7em-none-eabihf
Build crate
cargo build --release --target thumbv7em-none-eabihf --no-default-features
Results on my machine:
$ cargo build --release --target thumbv7em-none-eabihf --no-default-features
Compiling typenum v1.10.0
Compiling cc v1.0.37
Compiling byteorder v1.3.1
Compiling rand_core v0.4.0
Compiling subtle v2.1.0
Compiling rand_core v0.3.1
Compiling generic-array v0.12.0
Compiling digest v0.8.0
Compiling clear_on_drop v0.2.3
Compiling curve25519-dalek v1.1.4
Compiling no_std_test_lib v0.1.0 (.../no_std_test_lib)
Finished release [optimized] target(s) in 12.63s