Fix ice for feature-gated cfg attributes applied to the crate

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

compiler/rustc_attr_parsing/src/lib.rs

@@ -95,7 +95,7 @@ pub use attributes::cfg_old::*;
 pub use attributes::util::{
     find_crate_name, is_builtin_attr, is_doc_alias_attrs_contain_symbol, parse_version,
 };
-pub use context::{AttributeParser, Early, Late, OmitDoc};
+pub use context::{AttributeParser, Early, Late, OmitDoc, ShouldEmit};
 pub use lints::emit_attribute_lint;
 
 rustc_fluent_macro::fluent_messages! { "../messages.ftl" }