[BUG] GCC optimizes away the write with `benchmark::DoNotOptimize`

GCC16.1 optimizes away the write when we use `benchmark::DoNotOptimize`.

## Minimal reproducible example
```cpp
void f() {
int *a = new int[1 << 16];
for (int i = 0; i < 1 << 16; i++) {
benchmark::DoNotOptimize(a[i] = 10); // this is optimized away by the compiler
}
delete[] a;
}
```

Compiler explorer(CE) link: https://godbolt.org/z/j538536ss. The CE link contains a possible fix for the issue.

Start with the minimal reproducer in the issue and inspect the implementation of benchmark::DoNotOptimize, using the linked Compiler Explorer example to compare GCC 16.1 output. Done means the write in the loop is no longer optimized away while preserving the intended DoNotOptimize behavior.

Written by the indexing model from the issue text.