ntdll: fix compile for OpenBSD

[Austin English]

-- 
-Austin
-------------- next part --------------
diff --git a/dlls/ntdll/cdrom.c b/dlls/ntdll/cdrom.c
index a967f9c..df353e6 100644
--- a/dlls/ntdll/cdrom.c
+++ b/dlls/ntdll/cdrom.c
@@ -1938,7 +1938,9 @@ static NTSTATUS DVD_GetRegion(int dev, PDVD_REGION region)
  */
 static NTSTATUS DVD_ReadStructure(int dev, const DVD_READ_STRUCTURE *structure, PDVD_LAYER_DESCRIPTOR layer)
 {
-#ifdef DVD_READ_STRUCT
+#if defined(DVD_READ_STRUCT) && defined(__OpenBSD__)
+    union dvd_struct s;
+#elif defined(DVD_READ_STRUCT)
     dvd_struct s;
 
     if (structure->BlockByteOffset.u.HighPart || structure->BlockByteOffset.u.LowPart)