[Bug tree-optimization/114999] A few missing optimizations due to `a - b` and `b - a` not being detected as negatives of each other

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114999

--- Comment #16 from Drea Pinski <pinskia at gcc dot gnu.org> ---
An other example (related to comment #13):
```
int f(unsigned char a, unsigned char b)
{
  int aa = a;
  int bb = b;
  return a > b ? (aa-bb) : (bb - aa);
}
int f1(unsigned char a, unsigned char b)
{
  return a > b ? (a-b) : (b - a);
}
```