Make panic_fmt lint work properly for assert!(expr, msg) too.

Author: m-ou-se

core/src/macros/mod.rs

@@ -1216,6 +1216,7 @@ pub(crate) mod builtin {
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_builtin_macro]
     #[macro_export]
+    #[rustc_diagnostic_item = "assert_macro"]
     macro_rules! assert {
         ($cond:expr $(,)?) => {{ /* compiler built-in */ }};
         ($cond:expr, $($arg:tt)+) => {{ /* compiler built-in */ }};