[caffe2] fix clang build
Summary:
* multiple -Wpessimizing-moves
* `static` within `__host__` `__device__` function
Test Plan:
```lang=bash
buck build -c fbcode.cuda_use_clang=true fblearner/flow/projects/dper:workflow
```
Reviewed By: andrewjcg
Differential Revision: D23506573
fbshipit-source-id: 1490a1267e39e067d3ef836ef9b1cd5d7a28f724
