Support linux arm64 prebuilt protoc

Currently it looks as if there's a select in https://github.com/stackb/rules_proto/blob/5428336c51f18ad628d9c8d7e052a48ec5379590/toolchain/BUILD.bazel#L41 which doesn't take arch into consideration, which means it's not possible to run on arm64 linux.