change gradle build to use static libtorch + gc-sections (#25984)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25984
Link static libtorch libraries into pytorch.so (API library for android)
with "-Wl,--gc-sections" flag to remove unused symbols in libtorch.
Test Plan:
- full gradle CI with stacked PR;
- will check final artifacts.tgz size change;
Differential Revision: D17312859
Pulled By: ljk53
fbshipit-source-id: 99584d15922867a7b3c3d661ba238a6f99f43db5
