Add finding thnvrtc_library into torchconfig.cmake (#22126)
Summary:
Fixes https://github.com/pytorch/pytorch/pull/21861#issuecomment-504805368
Pull Request resolved: https://github.com/pytorch/pytorch/pull/22126
Differential Revision: D15964930
Pulled By: ezyang
fbshipit-source-id: 0fb749784bec9af5a8ccbcf775fa7d9d4d34a4c6
