Commit explicit libtorch_python sources (#19607)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/19607
Explicit is better than implicit - it's pretty hard to debug where particular file is if it's not greppable.
As a follow up step - we should look whether we can just include build_variables.py in CMake directly to share setups of two build systems
Reviewed By: ezyang
Differential Revision: D15023348
fbshipit-source-id: 600ef2d1871bc28530c6a02681b284f7499904df
