Define system-wide GUID structure

sdk/xtdk/xtstruct.h

@@ -142,6 +142,7 @@ typedef struct _EFI_USB_DEVICE_PATH EFI_USB_DEVICE_PATH, *PEFI_USB_DEVICE_PATH;
 typedef struct _EFI_USB_WWID_DEVICE_PATH EFI_USB_WWID_DEVICE_PATH, *PEFI_USB_WWID_DEVICE_PATH;
 typedef struct _EFI_VENDOR_DEVICE_PATH EFI_VENDOR_DEVICE_PATH, *PEFI_VENDOR_DEVICE_PATH;
 typedef struct _EFI_VLAN_DEVICE_PATH EFI_VLAN_DEVICE_PATH, *PEFI_VLAN_DEVICE_PATH;
+typedef struct _GUID GUID, *PGUID;
 typedef struct _LIST_ENTRY LIST_ENTRY, *PLIST_ENTRY;
 typedef struct _LIST_ENTRY32 LIST_ENTRY32, *PLIST_ENTRY32;
 typedef struct _LIST_ENTRY64 LIST_ENTRY64, *PLIST_ENTRY64;