Gentoo's Bugzilla –
Attachment 569366 Details for
Bug 680622app-arch/lzip-1.21: /usr/lib/gcc/powerpc64-unknown-linux-gnu/8.2.0/include/g++-v8/type_traits:335:39: error: ‘__float128’ was not declared in this scope struct __is_floating_point_helper<__float128>