Enable accurate caller location reporting during panic in {Option, Result}::{unwrap, expect} with the following changes:

1. Support the #[track_caller] function attribute, which guarantees a function has access to the caller information.
2. Add an intrinsic function caller_location() (safe wrapper: Location::caller()) to retrieve the caller's source location.

#![feature(track_caller)]
use std::panic::Location;

#[track_caller]
fn unwrap(self) -> T {
    panic!("{}: oh no", Location::caller());
}

let n: Option<u32> = None;
let m = n.unwrap();

https://rust-lang.github.io/rfcs/2091-inline-semantic.html