Tentative fix for CUDA-10.2 windows build failures (#76204)
Summary:
`C10_UNUSED` somehow triggers segfault in some versions of NVCC that looks like something as follows:
```
caffe2\caffe2\operators\piecewise_linear_transform_op.h(65): internal error: assertion failed: gen_variable_decl: declared_type is NULL (cp_gen_be.c, line 22209 in gen_variable_decl)
1 catastrophic error detected in the compilation of "caffe2/caffe2/operators/piecewise_linear_transform_op.cu".
Compilation aborted.
nvcc error : 'cudafe++' died with status 0xC0000409
```
Fixes regression introduced by https://github.com/pytorch/pytorch/pull/75538 / D35747333 (https://github.com/pytorch/pytorch/commit/f6c275f55ddfd22f8c0558efad3068b0e91f1560)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/76204
Test Plan: CI
Reviewed By: EscapeZero, atalman
Differential Revision: D35831451
fbshipit-source-id: f744d4688c9fd324f8f54b27781a3def97778d1e
(cherry picked from commit fd64655aa4b6890d205273ec76b416ee3b524783)
