.github: Add workflow to build libtorch (#53292)
Summary:
Based on https://github.com/pytorch/pytorch/issues/50633 and https://github.com/pytorch/pytorch/issues/51243.
Things left to do:
- [x] modify `.github/scripts/generate_binary_build_matrix.py` further
- [x] add option for not iterating over Python version
- [x] add `LIBTORCH_VARIANT`
- [x] add option for cxx11
- [x] fix the artifact uploading
- [x] remove `pull_request` hook before merging
Pull Request resolved: https://github.com/pytorch/pytorch/pull/53292
Test Plan: [CI](https://github.com/pytorch/pytorch/actions/runs/665781075).
Reviewed By: seemethere
Differential Revision: D27189150
Pulled By: samestep
fbshipit-source-id: ec91e1f0b75b8c93613d55801585ed975697be03
