cuda: allow C++17 build with CUDA 11+
Currently, trying to build with geant4@11 and CUDA fails when CMAKE_CXX_STANDARD is set to 17. (I encountered this building with spack and the cxxstd=17 flag.) This allows C++17 when using CUDA 11 or higher.
Currently, trying to build with geant4@11 and CUDA fails when CMAKE_CXX_STANDARD is set to 17. (I encountered this building with spack and the cxxstd=17 flag.) This allows C++17 when using CUDA 11 or higher.