Fix #if condition.

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

@@ -217,7 +217,7 @@ namespace System.Linq
             }
         }
 
-#if !(CSHARP8 && USE_ASYNC_ITERATOR)
+#if !(CSHARP8 && USE_ASYNC_ITERATOR && ASYNC_ITERATOR_CAN_RETURN_AETOR)
         private sealed class SelectEnumerableWithIndexAsyncIterator<TSource, TResult> : AsyncIterator<TResult>
         {
             private readonly Func<TSource, int, TResult> _selector;
@@ -523,7 +523,7 @@ namespace System.Linq
         }
 #endif
 
-#if !(CSHARP8 && USE_ASYNC_ITERATOR)
+#if !(CSHARP8 && USE_ASYNC_ITERATOR && ASYNC_ITERATOR_CAN_RETURN_AETOR)
         private sealed class SelectEnumerableWithIndexAsyncIteratorWithTask<TSource, TResult> : AsyncIterator<TResult>
         {
             private readonly Func<TSource, int, ValueTask<TResult>> _selector;

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

@@ -60,7 +60,7 @@ namespace System.Linq
 #endif
         }
 
-#if !(CSHARP8 && USE_ASYNC_ITERATOR)
+#if !(CSHARP8 && USE_ASYNC_ITERATOR && ASYNC_ITERATOR_CAN_RETURN_AETOR)
         private sealed class SkipLastAsyncIterator<TSource> : AsyncIterator<TSource>
         {
             private readonly int _count;

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

@@ -258,7 +258,7 @@ namespace System.Linq
         }
 #endif
 
-#if !(CSHARP8 && USE_ASYNC_ITERATOR)
+#if !(CSHARP8 && USE_ASYNC_ITERATOR && ASYNC_ITERATOR_CAN_RETURN_AETOR)
         private sealed class SkipWhileAsyncIterator<TSource> : AsyncIterator<TSource>
         {
             private readonly Func<TSource, bool> _predicate;

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

@@ -68,7 +68,7 @@ namespace System.Linq
 #endif
         }
 
-#if !(CSHARP8 && USE_ASYNC_ITERATOR)
+#if !(CSHARP8 && USE_ASYNC_ITERATOR && ASYNC_ITERATOR_CAN_RETURN_AETOR)
         private sealed class TakeLastAsyncIterator<TSource> : AsyncIterator<TSource>
         {
             private readonly int _count;

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

@@ -198,7 +198,7 @@ namespace System.Linq
         }
 #endif
 
-#if !(CSHARP8 && USE_ASYNC_ITERATOR)
+#if !(CSHARP8 && USE_ASYNC_ITERATOR && ASYNC_ITERATOR_CAN_RETURN_AETOR)
         private sealed class TakeWhileAsyncIterator<TSource> : AsyncIterator<TSource>
         {
             private readonly Func<TSource, bool> _predicate;

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

@@ -228,7 +228,7 @@ namespace System.Linq
             }
         }
 
-#if !(CSHARP8 && USE_ASYNC_ITERATOR)
+#if !(CSHARP8 && USE_ASYNC_ITERATOR && ASYNC_ITERATOR_CAN_RETURN_AETOR)
         private sealed class WhereEnumerableWithIndexAsyncIterator<TSource> : AsyncIterator<TSource>
         {
             private readonly Func<TSource, int, bool> _predicate;
@@ -428,7 +428,7 @@ namespace System.Linq
         }
 #endif
 
-#if !(CSHARP8 && USE_ASYNC_ITERATOR)
+#if !(CSHARP8 && USE_ASYNC_ITERATOR && ASYNC_ITERATOR_CAN_RETURN_AETOR)
         private sealed class WhereEnumerableWithIndexAsyncIteratorWithTask<TSource> : AsyncIterator<TSource>
         {
             private readonly Func<TSource, int, ValueTask<bool>> _predicate;

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

@@ -103,7 +103,7 @@ namespace System.Linq
         }
 #endif
 
-#if !(CSHARP8 && USE_ASYNC_ITERATOR)
+#if !(CSHARP8 && USE_ASYNC_ITERATOR && ASYNC_ITERATOR_CAN_RETURN_AETOR)
         private sealed class ZipAsyncIterator<TFirst, TSecond, TResult> : AsyncIterator<TResult>
         {
             private readonly IAsyncEnumerable<TFirst> _first;