torch.gcd: Do not use std::abs() because it does not have an unsigned integer overload (#42254)
Summary:
`abs` doesn't have an signed overload across all compilers, so applying abs on uint8_t can be ambiguous: https://en.cppreference.com/w/cpp/numeric/math/abs
This may cause unexpected issue when the input is uint8 and is greater
than 128. For example, on MSVC, applying `std::abs` on an unsigned char
variable
```c++
#include <cmath>
unsigned char a(unsigned char x) {
return std::abs(x);
}
```
gives the following warning:
warning C4244: 'return': conversion from 'int' to 'unsigned char',
possible loss of data
Pull Request resolved: https://github.com/pytorch/pytorch/pull/42254
Reviewed By: VitalyFedyunin
Differential Revision: D22860505
Pulled By: mruberry
fbshipit-source-id: 0076d327bb6141b2ee94917a1a21c22bd2b7f23a
