rpcrt4: Add a stub for RpcCancelThreadEx.

include/rpcdce.h

diff --git a/include/rpcdce.h b/include/rpcdce.h
index 1b8b6e7..79716ae 100644
--- a/include/rpcdce.h
+++ b/include/rpcdce.h
@@ -469,6 +469,7 @@
 #define RpcBindingInqAuthInfo WINELIB_NAME_AW(RpcBindingInqAuthInfo)
 
 RPCRTAPI RPC_STATUS RPC_ENTRY RpcCancelThread(void*);
+RPCRTAPI RPC_STATUS RPC_ENTRY RpcCancelThreadEx(void*,LONG);
 
 RPCRTAPI RPC_STATUS RPC_ENTRY
   RpcNetworkIsProtseqValidA( RPC_CSTR protseq );