Adding ENABLE_UNSTABLE option for rapids_cpm_cccl

[nirandaperera]

Description

This PR adds an ENABLE_UNSTABLE option to rapids_cpm_cccl, which will add cudax headers to the cmake build. Its set to OFF by default.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.
• The cmake-format.json is up to date with these changes.
• I have added new files under rapids-cmake/
  • I have added include guards (include_guard(GLOBAL))
  • I have added the associated docs/ rst file and update the api.rst

[bdice]

We’ll want to add some tests to this PR. Verify that the cudax target exists if the option is enabled, and doesn’t exist if it is disabled or not set. Maybe ask Cursor for help, there can be a fair amount of boilerplate in CMake…

[nirandaperera]

@bdice could you please add labels to this PR. I dont seem to have permission to update labels.

[bdice]

@robertmaynard or @KyleFromNVIDIA, would you be able to give this a review? It seems fine to me but I feel like there might be something else we need. Do we need any changes in cmake-format-rapids-cmake.json?

rapids-cmake/cmake-format-rapids-cmake.json

Lines 128 to 136 in d81225b

	"rapids_cpm_cccl": {
	"pargs": {
	"nargs": 0
	},
	"kwargs": {
	"BUILD_EXPORT_SET": 1,
	"INSTALL_EXPORT_SET": 1
	}
	},

[nirandaperera]

/merge

[KyleFromNVIDIA]

/merge