[Bug bootstrap/70200] builing gcc with -lfto without libunwind

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70200

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Why don't you use --with-build-config==bootstrap-lto as documented on
https://gcc.gnu.org/install/build.html .