unpredictable_function_pointer_comparisons doesn't lint against Option<fn()>

[kornelski]

In C FFI it's very common to use Option<fn()> for callbacks, but the lint #118833 doesn't fire when Options of function pointers are compared:

unsafe extern "C" fn func() {}

type FnPtr = unsafe extern "C" fn();

fn main() {
    assert_eq!(Some::<FnPtr>(func), Some(func as unsafe extern "C" fn()));
}

This pattern is used in: https://github.com/ImageOptim/mozjpeg-rust/blob/cff5aad77c726c11f460baefc348c7279d0ee647/src/readsrc.rs#L136

[Urgau]

Looks reasonable to me. Opened #134536