build-rootfs: Install baselayout first

The _sys-apps/baselayout_ package handles initializing a new filesystem
hierarchy.  With `USE=build`, it will create the appropriate symlinks in
`/` for a merged-usr tree.

build-rootfs.sh

@@ -7,22 +7,18 @@ set -e
 
 O="${1}"
 
-mkdir -p \
-    /mnt/gentoo/usr/bin \
-    /mnt/gentoo/usr/lib \
-    /mnt/gentoo/usr/lib64 \
-    || exit
-[ -h /mnt/gentoo/bin ] || ln -s usr/bin /mnt/gentoo/bin
-[ -h /mnt/gentoo/sbin ] || ln -s usr/sbin /mnt/gentoo/sbin
-[ -h /mnt/gentoo/usr/sbin ] || ln -s bin /mnt/gentoo/usr/sbin
-[ -h /mnt/gentoo/lib ] || ln -s usr/lib /mnt/gentoo/lib
-[ -h /mnt/gentoo/lib64 ] || ln -s usr/lib64 /mnt/gentoo/lib64
-
 mkdir -p /mnt/gentoo/etc/portage
 ln -snf \
     /var/db/repos/gentoo/profiles/${profile} \
     /mnt/gentoo/etc/portage/make.profile
 
+USE=build \
+emerge \
+    --root=/mnt/gentoo \
+    --config-root="${O}"/portage \
+    -kvnjU \
+    sys-apps/baselayout
+
 cat \
     install.packages \
     "${CONFIGDIR}"/install.packages \