CMAKE_CUDA_ARCHITECTURES: Support value for "none"
Some projects or packagers may want to specify compiler-specific architecture flags explicitly in e.g.
CMAKE_CUDA_FLAGS. With policy CMP0104's
NEW behavior, there is no longer a way to do this.
We could support the use case by using a special value for
CMAKE_CUDA_ARCHITECTURES, and therefore the
CUDA_ARCHITECTURES target property, that means "do not add any architecture flags". The value could be called
NONE or perhaps any of our typical boolean false values, like
0. That would allow packagers to use
... contains the architecture flags for the compiler in use.