Let users pass CMake-specific options starting with CMAKE_ to CMake. (#22776)
Summary:
This should make it more convenient to follow https://github.com/pytorch/pytorch/issues/8433's suggestion.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/22776
Differential Revision: D16222539
Pulled By: ezyang
fbshipit-source-id: 1cc6e69c85cdf0d7f8074653445410d85746847c
