[Bug libstdc++/86746] Libraries' configure uses config-ml.in whether multilib is being used or not

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86746

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I think on some targets (aarch64), multilib is always required.  In that the
libraries go in /lib64 always rather than /lib.