Keep track of whether extern type layout can be trusted
diff --git a/syntax/mod.rs b/syntax/mod.rs
index ae37802..e2356e1 100644
--- a/syntax/mod.rs
+++ b/syntax/mod.rs
@@ -48,6 +48,7 @@
     pub type_token: Token![type],
     pub ident: Ident,
     pub semi_token: Token![;],
+    pub trusted: bool,
 }
 
 pub struct Struct {