Port #[rustc_coherence_is_core] to the new attribute system

compiler/rustc_attr_data_structures/src/attributes.rs

@@ -214,6 +214,9 @@ pub enum AttributeKind {
         span: Span,
     },
 
+    /// Represents `#[rustc_coherence_is_core]`.
+    CoherenceIsCore,
+
     /// Represents `#[rustc_coinductive]`.
     Coinductive(Span),
 

compiler/rustc_attr_data_structures/src/encode_cross_crate.rs

@@ -19,6 +19,7 @@ impl AttributeKind {
             AllowInternalUnstable(..) => Yes,
             AsPtr(..) => Yes,
             BodyStability { .. } => No,
+            CoherenceIsCore => No,
             Coinductive(..) => No,
             Cold(..) => No,
             Confusables { .. } => Yes,