Port #[fundamental] to the new attribute system

compiler/rustc_attr_data_structures/src/attributes.rs

@@ -272,6 +272,9 @@ pub enum AttributeKind {
     /// Represents `#[ffi_pure]`.
     FfiPure(Span),
 
+    /// Represents `#[fundamental]`.
+    Fundamental,
+
     /// Represents `#[ignore]`
     Ignore {
         span: Span,

compiler/rustc_attr_data_structures/src/encode_cross_crate.rs

@@ -34,6 +34,7 @@ impl AttributeKind {
             ExportStable => No,
             FfiConst(..) => No,
             FfiPure(..) => No,
+            Fundamental { .. } => Yes,
             Ignore { .. } => No,
             Inline(..) => No,
             LinkName { .. } => Yes,