First try.

src/libraries/libmisc/ldifftime.c

+/*
+ * $Id: ldifftime.c,v 1.1 1994/04/04 13:51:23 ceder Exp $
+ * Copyright (C) 1994  Lysator Academic Computer Association.
+ *
+ * This file is part of the LysKOM server.
+ * 
+ * LysKOM is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by 
+ * the Free Software Foundation; either version 1, or (at your option) 
+ * any later version.
+ * 
+ * LysKOM is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with LysKOM; see the file COPYING.  If not, write to
+ * Lysator, c/o ISY, Linkoping University, S-581 83 Linkoping, SWEDEN,
+ * or the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, 
+ * MA 02139, USA.
+ *
+ * Please mail bug reports to bug-lyskom@lysator.liu.se. 
+ */
+
+#include <time.h>
+#include "ldifftime.h"
+
+extern long
+ldifftime(time_t t1, time_t t2)
+{
+#ifdef HAVE_DIFFTIME
+  return difftime (t1, t2);
+#else
+  return t1 - t2;
+#endif
+}

src/libraries/libmisc/ldifftime.h

+/*
+ * $Id: ldifftime.h,v 1.1 1994/04/04 13:51:31 ceder Exp $
+ * Copyright (C) 1994  Lysator Academic Computer Association.
+ *
+ * This file is part of the LysKOM server.
+ * 
+ * LysKOM is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by 
+ * the Free Software Foundation; either version 1, or (at your option) 
+ * any later version.
+ * 
+ * LysKOM is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with LysKOM; see the file COPYING.  If not, write to
+ * Lysator, c/o ISY, Linkoping University, S-581 83 Linkoping, SWEDEN,
+ * or the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, 
+ * MA 02139, USA.
+ *
+ * Please mail bug reports to bug-lyskom@lysator.liu.se. 
+ */
+
+#ifndef LDIFFTIME_H_INCLUDED
+#define LDIFFTIME_H_INCLUDED
+
+extern long
+ldifftime(time_t t1, time_t t2);
+
+#endif