Add missing trigramma_stub definition. (#30314)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/30314
Somehow we forgot to define it!
Signed-off-by: Edward Z. Yang <ezyang@fb.com>
Test Plan: Imported from OSS
Differential Revision: D18762356
Pulled By: ezyang
fbshipit-source-id: 28afc605ad986266071e3831049ec8a7f71fd695
