Mad the include files idempotent using a consistent macro naming
scheme.

diff --git a/include/struct32.h b/include/struct32.h
index 3c1c818..758f8d7 100644
--- a/include/struct32.h
+++ b/include/struct32.h
@@ -1,6 +1,6 @@
 /* Structure definitions for Win32 -- used only internally */
-#ifndef __WINE__STRUCT32_H
-#define __WINE__STRUCT32_H
+#ifndef __WINE_STRUCT32_H
+#define __WINE_STRUCT32_H
 
 #include "winbase.h"
 #include "wine/winuser16.h"