* configure.in (add_ons): Substitute this. Move $add_ons handling

* configure.in (add_ons): Substitute this.  Move $add_ons handling

	after AC_CANONICAL_HOST and default setting of $machine et al.
	Don't set $subdirs from $add_ons.
	Instead, source add-on/configure fragments early on.
	(base_machine): If it's already set, don't set it based on $machine.
	(libc_config_ok): New variable, set to no.  If an add-on fragment sets
	it to yes, skip the  tuple sanity check as if --enable-hacker-mode.
	(sysnames): Try appending add-on names after machine as well.
	* configure: Regenerated.
	* config.make.in (add-ons): Set from @add_ons@ instead of @subdirs@.
	* Makeconfig ($(common-objpfx)config.status): Also depend on configure
	files in $(add_ons) dirs.

	* sysdeps/unix/sysv/linux/bits/in.h (struct ip_mreq): Remove
	definition, now in netinet/in.h proper.

	long.  Rewrite example code so that it takes into account l64a output