Declare strdup.

lib/path-concat.c

@@ -1,5 +1,5 @@
 /* path-concat.c -- concatenate two arbitrary pathnames
-   Copyright (C) 1996, 1997, 1998, 1999 Free Software Foundation, Inc.
+   Copyright (C) 1996, 1997, 1998, 1999, 2000 Free Software Foundation, Inc.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -32,6 +32,7 @@
 #include <sys/types.h>
 
 char *malloc ();
+char *strdup ();
 
 #ifndef DIRECTORY_SEPARATOR
 # define DIRECTORY_SEPARATOR '/'