Consider a WORKSPACE `alias` rule

Something like:

WORKSPACE:
```
http_archive(
    name = "com_google_protobuf",
    ...
)

alias(
    name = "com_google_protobuf_cc",
    actual = "com_google_protobuf",
)
```

Depending on `com_google_protobuf_cc` would be equivalent to `com_google_protobuf`.

The use-case is highlighted in 
https://groups.google.com/forum/#!topic/bazel-discuss/859ybHQZnuI