Fix function inclusion with serde and no other default features

src/date.rs

@@ -3,6 +3,7 @@
 
 //! ISO 8601 calendar date with time zone.
 
+#[cfg(any(feature = "alloc", feature = "std", test))]
 use core::borrow::Borrow;
 use core::{fmt, hash};
 use core::cmp::Ordering;

src/datetime.rs

@@ -25,6 +25,7 @@ use format::{Item, Fixed};
 use format::{parse, Parsed, ParseError, ParseResult, StrftimeItems};
 #[cfg(any(feature = "alloc", feature = "std", test))]
 use format::DelayedFormat;
+#[cfg(any(feature = "alloc", feature = "std", test))]
 use core::borrow::Borrow;
 
 /// Specific formatting options for seconds. This may be extended in the

src/format/mod.rs

@@ -17,6 +17,7 @@
 
 #![allow(ellipsis_inclusive_range_patterns)]
 
+#[cfg(any(feature = "alloc", feature = "std", test))]
 use core::borrow::Borrow;
 use core::fmt;
 use core::str::FromStr;
@@ -365,6 +366,7 @@ pub fn format_item<'a>(
     w.pad(&result)
 }
 
+#[cfg(any(feature = "alloc", feature = "std", test))]
 fn format_inner<'a>(
     result: &mut String,
     date: Option<&NaiveDate>,