390bb3406d
Use panic() instead of panic!() in some places in core. See https://github.com/rust-lang/rust/pull/92068 and https://github.com/rust-lang/rust/pull/92140. This avoids the `panic!()` macro in a few potentially hot paths. This becomes more relevant when switching `core` to Rust 2021, as it'll avoid format_args!() and save some compilation time. (It doesn't make a huge difference, but still.) (Also the errors in const panic become slightly nicer.)