Added missing include file for windows after include the "sleep" function.

sqstdlib/sqstdsystem.cpp

@@ -3,7 +3,11 @@
 #include <time.h>
 #include <stdlib.h>
 #include <stdio.h>
-#include <sqstdsystem.h>
+#include <sqstdsystem.h>
+
+#ifdef _WIN32
+#include <windows.h>
+#endif
 
 #ifdef SQUNICODE
 #include <wchar.h>