Simplification for `(-a * b) / (a * b)` and `(-a + b) / (a - b)`

The following two functions can be evaluated as true.
```cpp
bool f(int a, int b)
{
   return (-a * b) / (a * b);
}

bool g(int a, int b)
{
   return (-a + b) / (a - b);
}
```

https://godbolt.org/z/sa5nTd9ob
https://alive2.llvm.org/ce/z/c5EBFp

GCC and MSVC can simplify the function `f`.