[FEA]: Add host only tests against libcu++

### Is this a duplicate?

- [X] I confirmed there appear to be no [duplicate issues](https://github.com/NVIDIA/cccl/issues) for this request and that I agree to the [Code of Conduct](CODE_OF_CONDUCT.md)

### Area

libcu++

### Is your feature request related to a problem? Please describe.

We want to ensure that we are able to build without nvcc as that is a valid usecase e.g for thrust.

### Describe the solution you'd like

We should ensure that our test suite can be run against only a host compiler. That will require some changes to our lit infrastructure

### Describe alternatives you've considered

_No response_

### Additional context

_No response_