c_deps/rust-sys

The BUILD files in this directory are for C dependencies that we have a fork of via a *-sys crate, e.g. rocksdb. Given we can make changes to the C source code via our fork, we cannot depend on the upstream versions of these libraries like we normally do. To build these special case C libraries we concatenate "additive" BUILD files to the ones generated by rules_rust/crate_repository.