Pin the versions of different Rust component packages to the same
version to ensure smooth upgrades. Not sure how to hook the compiler
together with the shared library. Likely rust-cross will need to provide
some kind of dependency to make this happen.
Convert libstd-rs to not use the shared source setup and instead use
its own extracted directory. Include the version info in the bitbake
file so that in the future we can support multiple versions via a
PREFERRED_VERSIONS variable.