Register CPU/CUDA fuser dynamically (#15887)
Summary:
This avoids a bunch of conditional compilation logic
Pull Request resolved: https://github.com/pytorch/pytorch/pull/15887
Reviewed By: eellison
Differential Revision: D13613239
Pulled By: zdevito
fbshipit-source-id: a18fc69676b3ef19b4469ab58d8714d1f6efccbb
