icpx fails test memory_scalar with -O3

With changes in PR: https://github.com/VcDevel/Vc/pull/292

## Testcase
```cpp
int main() {
    using V = Vc::native_simd<short>;
    Vc::Memory<V, 53> m1, m2;
    m1.setZero();
    m2.setZero();
    m1 += 1;
    return m1 != m2;
}
```

## Actual Results
0

## Expected Results
1

Godbolt: https://godbolt.org/z/8heTYahbf

The problem goes away if we use `-O2` instead of `-O3`.