Fix canonicalize_file_name clash.

canonicalize_file_name clashed with gnulib function. Additionally
it was declared in 2 places: emu/misc.h and util/misc.h. Added
grub_ prefix and removed second declaration.

grub-core/osdep/unix/relpath.c

@@ -44,7 +44,7 @@ grub_make_system_path_relative_to_its_root (const char *path)
   char *poolfs = NULL;
 
   /* canonicalize.  */
-  p = canonicalize_file_name (path);
+  p = grub_canonicalize_file_name (path);
   if (p == NULL)
     grub_util_error (_("failed to get canonical path of `%s'"), path);