Made the include files self-sufficient.

diff --git a/include/ntsecapi.h b/include/ntsecapi.h
index ec3a19f..662c101 100644
--- a/include/ntsecapi.h
+++ b/include/ntsecapi.h
@@ -2,6 +2,7 @@
 #define __WINE_NTSECAPI_H
 
 #include "ntdef.h"
+#include "winnt.h"
 
 #ifdef __cplusplus
 extern "C" {