Fix sign warnings in CUDA kernels (#66753)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/66753
Fixes these Wextra compilation errors:
```
stderr: caffe2/aten/src/ATen/native/cuda/UnarySignKernels.cu: In lambda function:
caffe2/aten/src/ATen/native/cuda/UnarySignKernels.cu:49:72: error: comparison is always false due to limited range of data type [-Werror=type-limits]
49 | AT_DISPATCH_ALL_TYPES_AND2 (https://github.com/pytorch/pytorch/commit/44fd312604fff5244e6d4fa1b3e440dd9b9e959f)(kBFloat16, ScalarType::Half, iter.input_dtype(), "signbit_cuda", [&]() {
| ~~^~~
stderr: caffe2/aten/src/ATen/native/cuda/BinaryMulDivKernel.cu: In lambda function:
caffe2/aten/src/ATen/native/cuda/BinaryMulDivKernel.cu:99:86: error: comparison is always false due to limited range of data type [-Werror=type-limits]
99 | AT_DISPATCH_INTEGRAL_TYPES(dtype, "div_floor_cuda", [&]() {
| ^
caffe2/aten/src/ATen/native/cuda/BinaryMulDivKernel.cu:99:97: error: comparison is always false due to limited range of data type [-Werror=type-limits]
99 | AT_DISPATCH_INTEGRAL_TYPES(dtype, "div_floor_cuda", [&]() {
| ^
stderr: caffe2/aten/src/ATen/native/cuda/BinaryMulDivKernel.cu: In lambda function:
caffe2/aten/src/ATen/native/cuda/BinaryMulDivKernel.cu:99:86: error: comparison is always false due to limited range of data type [-Werror=type-limits]
99 | AT_DISPATCH_INTEGRAL_TYPES(dtype, "div_floor_cuda", [&]() {
| ^
```
And also these warnings:
```
caffe2/c10/util/Half.h(461): warning: pointless comparison of unsigned integer with zero
detected during instantiation of "std::enable_if<<expression>, __nv_bool>::type c10::overflows<To,From>(From) [with To=size_t, From=unsigned long]"
caffe2/aten/src/ATen/native/Resize.h(45): here
caffe2/c10/util/Half.h(459): warning: pointless comparison of unsigned integer with zero
detected during instantiation of "std::enable_if<<expression>, __nv_bool>::type c10::overflows<To,From>(From) [with To=size_t, From=unsigned long]"
caffe2/aten/src/ATen/native/Resize.h(45): here
```
I thought I'd fixed this previously using `std::is_unsigned` in D25256251 (https://github.com/pytorch/pytorch/commit/cff1ff7fb6744dd6370ccccc5c90230ca3721140), but apparently that was insufficient.
Test Plan: Sandcastle
Reviewed By: malfet, ngimel
Differential Revision: D31708173
fbshipit-source-id: 7714f6bbf109d2f2164630d3fc46bad18046c06c
