Just grab the code (and the Spike submodule).
Then run cmake . followed by make.
This will build Spike and the CPUTest executable.
You'll need to have CUDA installed.
Generally, I recommend having a separate 'build' directory
(If you want to do this, then do cd build; cmake ..; make).
(Otherwise, CMake will leave lots of clutter around in the top-level
source tree!)
Then just run ./CPUTest to make sure it functions!
Have a look in CMakeLists.txt to see how the build works.