Port #[rustc_allow_incoherent_impl] to the new attribute system

compiler/rustc_attr_data_structures/src/attributes.rs

@@ -198,6 +198,9 @@ pub enum AttributeKind {
     /// Represents `#[rustc_allow_const_fn_unstable]`.
     AllowConstFnUnstable(ThinVec<Symbol>, Span),
 
+    /// Represents `#[rustc_allow_incoherent_impl]`.
+    AllowIncoherentImpl(Span),
+
     /// Represents `#[allow_internal_unstable]`.
     AllowInternalUnstable(ThinVec<(Symbol, Span)>, Span),
 

compiler/rustc_attr_data_structures/src/encode_cross_crate.rs

@@ -15,6 +15,7 @@ impl AttributeKind {
             // tidy-alphabetical-start
             Align { .. } => No,
             AllowConstFnUnstable(..) => No,
+            AllowIncoherentImpl(..) => No,
             AllowInternalUnstable(..) => Yes,
             AsPtr(..) => Yes,
             BodyStability { .. } => No,