Implemented _CheckNotSysLevel.

diff --git a/include/winbase.h b/include/winbase.h
index 2ae06ca..e32946f 100644
--- a/include/winbase.h
+++ b/include/winbase.h
@@ -1918,6 +1918,7 @@
 void        WINAPI SetProcessDword(DWORD,INT,DWORD);
 VOID        WINAPI UnMapLS(DWORD);
 HFILE       WINAPI Win32HandleToDosFileHandle(HANDLE);
+VOID        WINAPI _CheckNotSysLevel(SYSLEVEL *lock);
 DWORD       WINAPI _ConfirmWin16Lock(void);
 DWORD       WINAPI _ConfirmSysLevel(SYSLEVEL*);
 VOID        WINAPI _EnterSysLevel(SYSLEVEL*);