use #[cfg(bootstrap)] for rustc sync

library/compiler-builtins/compiler-builtins/Cargo.toml

@@ -70,3 +70,6 @@ rustc-dep-of-std = ['compiler-builtins', 'core']
 # This makes certain traits and function specializations public that
 # are not normally public but are required by the `testcrate`
 public-test-deps = []
+
+[lints.rust]
+unexpected_cfgs = { level = "warn", check-cfg = ['cfg(bootstrap)'] }

library/compiler-builtins/compiler-builtins/src/macros.rs

@@ -433,6 +433,17 @@ macro_rules! intrinsics {
     ) => (
         // `#[naked]` definitions are referenced by other places, so we can't use `cfg` like the others
         pub mod $name {
+            // FIXME: when bootstrap supports `#[unsafe(naked)]` this duplication can be removed
+            #[cfg(bootstrap)]
+            #[naked]
+            $(#[$($attr)*])*
+            #[cfg_attr(not(feature = "mangled-names"), no_mangle)]
+            #[cfg_attr(not(any(all(windows, target_env = "gnu"), target_os = "cygwin")), linkage = "weak")]
+            pub unsafe extern $abi fn $name( $($argname: $ty),* ) $(-> $ret)? {
+                $($body)*
+            }
+
+            #[cfg(not(bootstrap))]
             #[unsafe(naked)]
             $(#[$($attr)*])*
             #[cfg_attr(not(feature = "mangled-names"), no_mangle)]