[Bug tree-optimization/126689] Missed removal of nested copysigns

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126689

--- Comment #5 from Drea Pinski <pinskia at gcc dot gnu.org> ---
```
double f3(double x, double y, double tt)
{
  double t = -__builtin_copysign (y, tt);
  return __builtin_copysign (x,t);
}
```

Should just be: __builtin_copysign (x,-tt);

Also.