Try to make the gentoo build faster

gentoo

-FROM gentoo/stage3-amd64
+FROM gentoo/portage:latest as portage
+FROM gentoo/stage3-amd64:latest
+
+COPY --from=portage /usr/portage /usr/portage
+
 ENV ACCEPT_KEYWORDS="~amd64" \
     EMERGE_DEFAULT_OPTS="--buildpkg --jobs=9 --load-average=8 --with-bdeps=y --usepkg" \
     MAKEOPTS="-j9 -l8" \