Fix nvcc warnings (#55367)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/55367
During compilation, nvcc emits several warnings about unused variables and static funcions:
```
caffe2/aten/src/ATen/native/cuda/SpectralOps.cu(231): warning: function "at::native::_run_cufft" was declared but never referenced
caffe2/aten/src/ATen/native/sparse/cuda/SparseMatMul.cu(60): warning: function "at::native::<unnamed>::confirm_mult_size" was declared but never referenced
caffe2/aten/src/ATen/native/cuda/UnaryFractionKernels.cu(112): warning: function "at::native::nearbyint_wrapper(c10::complex<double>)" was declared but never referenced
caffe2/aten/src/ATen/native/cuda/TensorFactories.cu(106): warning: variable "d_temp_storage" was declared but never referenced
caffe2/torch/fb/sparsenn/sparsenn_operators_gpu.cu(2325): warning: variable "kMaxThreads" was declared but never referenced
```
To reproduce, run the following build command on remote/master:
```
buck build mode/dev-nosan caffe2/torch/fb/sparsenn:sparsenn_operators_gpu
```
Warnings about unused variables are fixed by removing the variable declaration. However, I don't want to remove the unused static functions. They were probably used before some other part of the code was refactored. They might be useful again in the future. So, I added a #pragma firectives to disable warnings for such functions.
Test Plan: Compilation does not produce warnings any more.
Reviewed By: r-barnes
Differential Revision: D27577342
fbshipit-source-id: e6a6e5ec513996337d904985dd27c60601c74803
