Port #[rustc_paren_sugar] to the new attribute system

compiler/rustc_attr_data_structures/src/attributes.rs

@@ -325,6 +325,9 @@ pub enum AttributeKind {
     /// Represents `#[optimize(size|speed)]`
     Optimize(OptimizeAttr, Span),
 
+    /// Represents `#[rustc_paren_sugar]`.
+    ParenSugar(Span),
+
     /// Represents `#[rustc_pass_by_value]` (used by the `rustc_pass_by_value` lint).
     PassByValue(Span),
 

compiler/rustc_attr_data_structures/src/encode_cross_crate.rs

@@ -49,6 +49,7 @@ impl AttributeKind {
             NoMangle(..) => No,
             NonExhaustive(..) => Yes,
             Optimize(..) => No,
+            ParenSugar(..) => No,
             PassByValue(..) => Yes,
             Path(..) => No,
             PubTransparent(..) => Yes,