Eliminate the use of CUDA_HOME in setup.py. (#28373)
Summary:
Variables read from CMakeCache.txt are more reliable.
Close https://github.com/pytorch/pytorch/issues/28365
Pull Request resolved: https://github.com/pytorch/pytorch/pull/28373
Differential Revision: D18061855
Pulled By: ezyang
fbshipit-source-id: c550a365e23464411d75eca167f7e6e053f94872
