prevent generating caffe2::mkl for multiple times (#25167)
Summary:
fixes issue https://github.com/pytorch/pytorch/issues/25004
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25167
Differential Revision: D17051290
Pulled By: ezyang
fbshipit-source-id: 30c2b6d6ffca2ce8dae45a4a706ce45d6386c672
