Fix for 32-bit windows.

Is there really someone use this?

Author: Berrysoft

src/driver/iocp/op.rs

@@ -93,7 +93,10 @@ impl<T: IoBufMut> OpCode for ReadAt<T> {
     unsafe fn operate(&mut self, optr: *mut OVERLAPPED) -> Poll<io::Result<usize>> {
         if let Some(overlapped) = optr.as_mut() {
             overlapped.Anonymous.Anonymous.Offset = (self.offset & 0xFFFFFFFF) as _;
-            overlapped.Anonymous.Anonymous.OffsetHigh = (self.offset >> 32) as _;
+            #[cfg(target_pointer_width = "64")]
+            {
+                overlapped.Anonymous.Anonymous.OffsetHigh = (self.offset >> 32) as _;
+            }
         }
         let slice = self.buffer.as_uninit_slice();
         let res = ReadFile(
@@ -111,7 +114,10 @@ impl<T: IoBuf> OpCode for WriteAt<T> {
     unsafe fn operate(&mut self, optr: *mut OVERLAPPED) -> Poll<io::Result<usize>> {
         if let Some(overlapped) = optr.as_mut() {
             overlapped.Anonymous.Anonymous.Offset = (self.offset & 0xFFFFFFFF) as _;
-            overlapped.Anonymous.Anonymous.OffsetHigh = (self.offset >> 32) as _;
+            #[cfg(target_pointer_width = "64")]
+            {
+                overlapped.Anonymous.Anonymous.OffsetHigh = (self.offset >> 32) as _;
+            }
         }
         let slice = self.buffer.as_slice();
         let res = WriteFile(