This PR adds support for detecting if overflow checks are enabled in similar fashion as debug_assertions are detected.
Possible use-case of this, for example, if we want to use checked integer casts in builds with overflow checks, e.g.
```rust
pub fn cast(val: usize)->u16 {
if cfg!(overflow_checks) {
val.try_into().unwrap()
}
else{
vas as _
}
}
```
Resolves#91130.
Tracking issue: #111466.
Negating a non-zero integer currently requires unpacking to a
primitive and re-wrapping. Since negation of non-zero signed
integers always produces a non-zero result, it is safe to
implement `Neg` for `NonZeroI{N}`.
The new `impl` is marked as stable because trait implementations
for two stable types can't be marked unstable.
