Port #[export_name] to the new attribute parsing infrastructure

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

compiler/rustc_attr_data_structures/src/encode_cross_crate.rs

@@ -22,6 +22,7 @@ impl AttributeKind {
             ConstStabilityIndirect => No,
             Deprecation { .. } => Yes,
             DocComment { .. } => Yes,
+            ExportName { .. } => Yes,
             Inline(..) => No,
             MacroTransparency(..) => Yes,
             Repr(..) => No,