Update Cross config for v0.2.2 (#3286)
Update Cross config for v0.2.2 (#3286)

## Proposed Changes

Update `Cross.toml` for the recently released Cross v0.2.2. This allows us to remove the dependency on my fork of the Cross Docker image, which was a maintenance burden and prone to bit-rot. This PR puts us back in sync with upstream Cross.

## Additional Info

Due to some bindgen errors on the default Cross images we seemingly need a full `clang-3.9` install. The `libclang-3.9-dev` package was found to be insufficient due to `stdarg.h` being missing.

In order to continue building locally all Lighthouse devs should update their local cross version with `cargo install cross`.




sigp/lighthouse,sigp/lighthouse,sigp/lighthouse,sigp/lighthouse