der: provide a noop implementation for PhantomData

similar to #1009, provide a `der::DerOrd` and a `der::ValueOrd` noop
implementation for PhantomData

Author: baloo

der/src/ord.rs

@@ -1,7 +1,7 @@
 //! Ordering trait.
 
 use crate::{EncodeValue, Result, Tagged};
-use core::cmp::Ordering;
+use core::{cmp::Ordering, marker::PhantomData};
 
 /// DER ordering trait.
 ///
@@ -69,3 +69,17 @@ where
 
     Ok(length_ord)
 }
+
+/// Provide a no-op implementation for PhantomData
+impl<T> ValueOrd for PhantomData<T> {
+    fn value_cmp(&self, _other: &Self) -> Result<Ordering> {
+        Ok(Ordering::Equal)
+    }
+}
+
+/// Provide a no-op implementation for PhantomData
+impl<T> DerOrd for PhantomData<T> {
+    fn der_cmp(&self, _other: &Self) -> Result<Ordering> {
+        Ok(Ordering::Equal)
+    }
+}