Add linting for `crate_type` attribute values.

This ensures that the `crate_type` attribute always contains a value,
and does not contain an invalid value.
auto merge of #11264 : am0d/rust/crate_type_lint, r=alexcrichton

This ensures that the `crate_type` attribute always contains a value,
and does not contain an invalid value.

Fixes #11256.