Fix libgfortran for NaCl.

libgfortran/runtime/main.c

 /* Copyright (C) 2002-2003, 2005, 2007, 2009 Free Software Foundation, Inc.
    Contributed by Andy Vaught and Paul Brook <paul@nowt.org>
 
 This file is part of the GNU Fortran 95 runtime library (libgfortran).
 
 Libgfortran 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 3, or (at your option)
 any later version.
 
@@ skipping 99 matching lines @@
   if (argv0 == NULL || argv0[0] == '/')
     {
       exe_path = argv0;
       please_free_exe_path_when_done = 0;
       return;
     }
 
   memset (buf, 0, sizeof (buf));
 #ifdef HAVE_GETCWD
   cwd = getcwd (buf, sizeof (buf));
+  if (cwd == NULL)
+    {
+      cwd = "";
+    }
 #else
   cwd = "";
 #endif
 
   /* exe_path will be cwd + "/" + argv[0] + "\0" */
   path = malloc (strlen (cwd) + 1 + strlen (argv0) + 1);
   sprintf (path, "%s%c%s", cwd, DIR_SEPARATOR, argv0);
   exe_path = path;
   please_free_exe_path_when_done = 1;
 }
@@ skipping 36 matching lines @@
 /* Cleanup the runtime library.  */
 
 static void __attribute__((destructor))
 cleanup (void)
 {
   close_units ();
   
   if (please_free_exe_path_when_done)
     free ((char *) exe_path);
 }