* Add CMake options for building with CUDA/HIP support to
CachedCMakePackages (intended to reduce duplication across packages
building with +hip/+cuda and using CachedCMakePackage)
* Define generic variables like CMAKE_PREFIX_PATH for
CachedCMakePackages (so that a user may invoke "cmake" themselves
without needing to setthem on the command line).
* Make `lbann` a CachedCMakePackage.
Co-authored-by: Chris White <white238@llnl.gov>
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