pytorch

501d0729 - move build_variables.bzl and ufunc_defs.bzl from pytorch-root/tools/ to the root

move build_variables.bzl and ufunc_defs.bzl from pytorch-root/tools/ to the root Pull Request resolved: https://github.com/pytorch/pytorch/pull/78542 This makes importing easier in different build systems that have different absolute names for the pytorch-root. Differential Revision: [D36782582](https://our.internmc.facebook.com/intern/diff/D36782582/) **NOTE FOR REVIEWERS**: This PR has internal Facebook specific changes or comments, please review them on [Phabricator](https://our.internmc.facebook.com/intern/diff/D36782582/)! Approved by: https://github.com/malfet