Turn on Werror for deprecated-declarations. (#21195)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/21195
The motivation is that, while we shouldn't break USER code for using
deprecated declarations, we should keep our internal code base
deprecation clean.
Differential Revision: D15576968
fbshipit-source-id: fb73a8986a5b60bf49ee18260653100319bb1030
