include/winspool: Declare missing function.

include/winspool.h

diff --git a/include/winspool.h b/include/winspool.h
index 297cb22..a642eef 100644
--- a/include/winspool.h
+++ b/include/winspool.h
@@ -1389,6 +1389,10 @@
 LPWSTR WINAPI StartDocDlgW(HANDLE hPrinter, DOCINFOW *doc);
 #define StartDocDlg WINELIB_NAME_AW(StartDocDlg)
 
+BOOL WINAPI XcvDataW(HANDLE hXcv, LPCWSTR pszDataName, PBYTE pInputData,
+    DWORD cbInputData, PBYTE pOutputData, DWORD cbOutputData,
+    PDWORD pcbOutputNeeded, PDWORD pdwStatus);
+
 #ifdef __cplusplus
 } /* extern "C" */
 #endif