[DOC]: Document relevant CCCL macros

[fbusato]

Is this a duplicate?

• [x] I confirmed there appear to be no duplicate issues for this bug and that I agree to the Code of Conduct

Is this for new documentation, or an update to existing docs?

New

Describe the incorrect/future/missing documentation

CCCL macros are very curated and are tested across many configurations in all projects that adopt CCCL. Some examples:

• host/device: _CCCL_HOST_DEVICE
• standard attributes: _CCCL_FALLTHROUGH, _CCCL_NODISCARD
• compiler macros: _CCCL_CUDA_COMPILER
• buildins: _CCCL_HAS_BUILTIN
• dialects: _CCCL_STD_VER,
• etc.

These macros can be documented and exposed to users

If this is a correction, please provide a link to the incorrect documentation. If this is a new documentation request, please link to where you have looked.

https://nvidia.github.io/cccl/libcudacxx/extended_api/macro.html