expand: Support helper attributes for built-in derive macros

Author: petrochenkov

core/src/macros/mod.rs

@@ -1,6 +1,7 @@
 #[doc = include_str!("panic.md")]
 #[macro_export]
-#[rustc_builtin_macro = "core_panic"]
+#[cfg_attr(bootstrap, rustc_builtin_macro = "core_panic")]
+#[cfg_attr(not(bootstrap), rustc_builtin_macro(core_panic))]
 #[allow_internal_unstable(edition_panic)]
 #[stable(feature = "core", since = "1.6.0")]
 #[rustc_diagnostic_item = "core_panic_macro"]

std/src/macros.rs

@@ -6,7 +6,8 @@
 
 #[doc = include_str!("../../core/src/macros/panic.md")]
 #[macro_export]
-#[rustc_builtin_macro = "std_panic"]
+#[cfg_attr(bootstrap, rustc_builtin_macro = "std_panic")]
+#[cfg_attr(not(bootstrap), rustc_builtin_macro(std_panic))]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[allow_internal_unstable(edition_panic)]
 #[cfg_attr(not(test), rustc_diagnostic_item = "std_panic_macro")]