lstopo: only show interactive help if stdout is a tty

Otherwise things like .xsession-errors (depending on the window manager)
might get flooded with those messages.

Ignored on Windows since I have now idea where those messages go
when the app doesn't run from a terminal.

Signed-off-by: Brice Goglin <Brice.Goglin@inria.fr>

utils/lstopo/lstopo.c

@@ -577,9 +577,11 @@ void usage(const char *name, FILE *where)
 
 void lstopo_show_interactive_help(void)
 {
+#ifdef HAVE_ISATTY
   if (!isatty(STDOUT_FILENO))
     /* don't send the interactive help when not a terminal */
     return;
+#endif
 
   printf("\n");
   printf("Keyboard shortcuts:\n");