Don't try to recover keyword as non-keyword identifier

There's no sensible recovery scheme here, giving up the recovery is the
right thing to do.

(cherry picked from commit 79c47278f1)

compiler/rustc_parse/src/parser/item.rs

@@ -393,6 +393,7 @@ impl<'a> Parser<'a> {
         let insert_span = ident_span.shrink_to_lo();
 
         let ident = if self.token.is_ident()
+            && self.token.is_non_reserved_ident()
             && (!is_const || self.look_ahead(1, |t| *t == token::OpenParen))
             && self.look_ahead(1, |t| {
                 matches!(t.kind, token::Lt | token::OpenBrace | token::OpenParen)