FindCUDA: Use find_program instead of find_path to find nvcc (#29160)
Summary:
Otherwise nvcc is not found if it is in env PATH but a non-standard
location.
Import from my patch for CMake:
https://gitlab.kitware.com/cmake/cmake/merge_requests/3990
Although we currently do nvcc search in a Python script, it will be removed soon in https://github.com/pytorch/pytorch/issues/28617.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/29160
Differential Revision: D18326693
Pulled By: ezyang
fbshipit-source-id: dc7ff3f6026f0655386ff685bce7372e2b061a4b
