Fix ICE for parsed attributes with longer path not handled by CheckAttrVisitor

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

compiler/rustc_attr_parsing/src/context.rs

@@ -718,6 +718,11 @@ impl<'sess, S: Stage> AttributeParser<'sess, S> {
         attributes
     }
 
+    /// Returns whether there is a parser for an attribute with this name
+    pub fn is_parsed_attribute(path: &[Symbol]) -> bool {
+        Late::parsers().0.contains_key(path)
+    }
+
     fn lower_attr_args(&self, args: &ast::AttrArgs, lower_span: impl Fn(Span) -> Span) -> AttrArgs {
         match args {
             ast::AttrArgs::Empty => AttrArgs::Empty,