Fixed the following errors when building v7.8.0 source published on PyPI:
RuntimeError: Missing file: cupy/cuda/cub.cpp(when CUB is configured via the environment variable or using CUDA 11.0)RuntimeError: Missing file: cupy/cuda/cutensor.cpp(when cuTENSOR is configured via the environment variable)
This release is only for packaging fix; there is no code difference since v7.8.0.