[Bug libquadmath/85440] libquadmath and quadmath.h do not exist on ppc64

[meissner at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85440

--- Comment #13 from Michael Meissner <meissner at gcc dot gnu.org> ---
You can use --with-cpu=power7 as well.  But if you only have power8 systems, it
is better to use --with-cpu=power8.  The little endian PowerPC Linux systems
have a minimum cpu base level of power8, so float128 is available on that
platform by default.