Add link to pull request.

Ix.NET/Source/System.Linq.Async/System/Linq/Operators/Except.cs

@@ -20,7 +20,7 @@ namespace System.Linq
             if (second == null)
                 throw Error.ArgumentNull(nameof(second));
 
-#if CSHARP8 && USE_ASYNC_ITERATOR && ASYNC_ITERATOR_CAN_RETURN_AETOR
+#if CSHARP8 && USE_ASYNC_ITERATOR && ASYNC_ITERATOR_CAN_RETURN_AETOR // https://github.com/dotnet/roslyn/pull/31114
             return Create(Core);
 
             async IAsyncEnumerator<TSource> Core(CancellationToken cancellationToken)

Ix.NET/Source/System.Linq.Async/System/Linq/Operators/Intersect.cs

@@ -20,7 +20,7 @@ namespace System.Linq
             if (second == null)
                 throw Error.ArgumentNull(nameof(second));
 
-#if CSHARP8 && USE_ASYNC_ITERATOR && ASYNC_ITERATOR_CAN_RETURN_AETOR
+#if CSHARP8 && USE_ASYNC_ITERATOR && ASYNC_ITERATOR_CAN_RETURN_AETOR // https://github.com/dotnet/roslyn/pull/31114
             return Create(Core);
 
             async IAsyncEnumerator<TSource> Core(CancellationToken cancellationToken)