Bundled Kokkos + CUDA

[drwells]

It looks like we can't configure our bundled copy of Kokkos to use CUDA - is this expected? I see the following message:

-- DEAL_II_WITH_KOKKOS has unmet external dependencies.
-- 
-- DEAL_II_WITH_KOKKOS successfully set up with bundled packages.
-- 
-- Include /home/drwells/Documents/Code/CPP/dealii/cmake/configure/configure_40_cuda.cmake
-- DEAL_II_WITH_CUDA has unmet external dependencies.
CMake Error at cmake/configure/configure_40_cuda.cmake:103 (message):
  

  Could not find any suitable cuda library!

  deal.II can only be compiled with Cuda support if Kokkos was built with
  Cuda support!

How hard would it be to build our own Kokkos with CUDA support? I would like to do this so I can test step-64.

[masterleinad]

We hardcode the Kokkos configuration to only provide the Serial backend for the bundled Kokkos copy so that we can avoid running Kokkos whole CMake configuration. It's not feasible to support building different backends if we don't commit to use Kokkos' build system.
If you want to test step-64, I would just use an external Kokkos installation (although step-64 shouldn't really need Cuda support anymore anyway) like we do in our CI

dealii/.github/workflows/linux.yml

Lines 151 to 169 in a740622

	- uses: actions/checkout@v3
	with:
	repository: kokkos/kokkos
	ref: 3.7.00
	path: kokkos
	- name: compile and install kokkos
	working-directory: kokkos
	run: |
	mkdir build
	cd build
	cmake -D BUILD_SHARED_LIBS=ON \
	-D CMAKE_CXX_COMPILER=${GITHUB_WORKSPACE}/kokkos/bin/nvcc_wrapper \
	-D CMAKE_INSTALL_PREFIX=${GITHUB_WORKSPACE}/../kokkos-install \
	-D Kokkos_ENABLE_CUDA=ON \
	-D Kokkos_ENABLE_CUDA_LAMBDA=ON \
	-D Kokkos_ENABLE_CUDA_CONSTEXPR=ON \
	-D Kokkos_ARCH_VOLTA70=ON \
	..
	make install

.

[drwells]

Thanks - I'll try that out and also see if I can put a better error message in the build system.