[BUG]: Improve cuda/std/cmath to build without depending on the relaxed constexpr build option

[PointKernel]

Is this a duplicate?

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

Type of Bug

Compile-time Error

Component

libcu++

Describe the bug

While working on building libcudf without enabling the relaxed constexpr option (rapidsai/cudf#7795), I observed that several
cuda/std/cmath utilities cannot be built without relying on the relaxed constexpr option.

How to Reproduce

See https://godbolt.org/z/f5ebG1Wxz

Expected behavior

The above godbolt should work without errors

Reproduction link

https://godbolt.org/z/f5ebG1Wxz

[miscco]

Yeah that is an unfortunate historical artefact. We started properly implementing all the math functions, but it is a ... process

[PointKernel]

@miscco Thanks for getting the PR up so quickly!

Quick question: Will the corresponding PR make cuda::std::ceil a constexpr when building with NVCC 11.8?
https://godbolt.org/z/94nYnvqMW

[miscco]

Need to check whether the compiler supports it but my guess is no

[miscco]

Merged the fixes, those functions should now be available