Use CMAKE_CUDA_ARCHITECTURES value when ENV{CUDAARCHS} is set

[robertmaynard]

Description

When a user has both the env variable and CMake command line cache value specified we need to ensure that the users cache value is used.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.

[bdice]

Is the choice of deprioritizing environment variables consistent with how CMake handles other variables? Do we need a documentation update to explain the order of preference?

[KyleFromNVIDIA]

Is the choice of deprioritizing environment variables consistent with how CMake handles other variables?

Yes.

Do we need a documentation update to explain the order of preference?

Wouldn't be a bad idea.

[robertmaynard]

Is the choice of deprioritizing environment variables consistent with how CMake handles other variables? Do we need a documentation update to explain the order of preference?

This aligns rapids-cmake with CMake's evaluation rules:

$ CUDAARCHS=80  cmake -S . -B build -DCMAKE_CUDA_ARCHITECTURES="75-real" && cat build/CMakeCache.txt | grep CMAKE_CUDA_ARCHITECTURES
-- The CXX compiler identification is GNU 9.4.0
-- The C compiler identification is GNU 9.4.0
-- The CUDA compiler identification is NVIDIA 12.4.131
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CUDA compiler ABI info
-- Detecting CUDA compiler ABI info - done
-- Check for working CUDA compiler: /usr/local/cuda/bin/nvcc - skipped
-- Detecting CUDA compile features
-- Detecting CUDA compile features - done
-- foo_lib: foo_lib-NOTFOUND
-- Configuring done (1.5s)
-- Generating done (0.0s)
-- Build files have been written to: ..../build
CMAKE_CUDA_ARCHITECTURES:STRING=75-real