Summary:
Symbols are given hidden visibility by default on Linux to emulate the behavior on Windows.  This helps developers catch visibility issues in their streamlined Linux dev environment before being surprised, late in the process, by Windows errors.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20461

Reviewed By: kostmo

Differential Revision: D15410410

Pulled By: dzhulgakov

fbshipit-source-id: 1d684b5a9a80b692966a775c3f1c56b7c72ffc95