Rust doesn't have __FUNCTION__ or __func__ (though you can hack around it with a
proc macro, but that will require a separate crate and slowing down compilation
times with heavy proc macro dependencies), so these are just regular functions
(at least for now). Rust's default stack trace on panic (even in release mode)
should be enough (and the functions themselves are inlined so the calling
function should be the second frame from the top, after the #[cold] panic
functions).