Port #[ignore] to the new attribute parsing infrastructure

Signed-off-by: Jonathan Brouwer <jonathantbrouwer@gmail.com>

compiler/rustc_attr_data_structures/src/attributes.rs

@@ -250,6 +250,13 @@ pub enum AttributeKind {
         span: Span,
     },
 
+    /// Represents `#[ignore]`
+    Ignore {
+        span: Span,
+        /// ignore can optionally have a reason: `#[ignore = "reason this is ignored"]`
+        reason: Option<Symbol>,
+    },
+
     /// Represents `#[inline]` and `#[rustc_force_inline]`.
     Inline(InlineAttr, Span),
 

compiler/rustc_attr_data_structures/src/encode_cross_crate.rs

@@ -26,6 +26,7 @@ impl AttributeKind {
             Deprecation { .. } => Yes,
             DocComment { .. } => Yes,
             ExportName { .. } => Yes,
+            Ignore { .. } => No,
             Inline(..) => No,
             LinkName { .. } => Yes,
             LinkSection { .. } => No,