Change struct expr pretty printing to match rustfmt style

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -1,3 +1,4 @@
+mod delimited;
 mod expr;
 mod item;
 
@@ -23,6 +24,8 @@ use rustc_span::{BytePos, FileName, Span};
 
 use std::borrow::Cow;
 
+pub use self::delimited::IterDelimited;
+
 pub enum MacHeader<'a> {
     Path(&'a ast::Path),
     Keyword(&'static str),