build-rootfs: Relocate misplaced PAM libs

Some packages, notably _systemd_, place their PAM modules in
`/usr/lib64/security` instead of `/usr/lib/security`.  PAM only seems to
look in the latter location, though, so anything in the former needs to
be moved in order to be used.

build-rootfs.sh

@@ -76,11 +76,23 @@ if [ -f /mnt/gentoo/etc/udev/hwdb.bin ]; then
     mv /mnt/gentoo/etc/udev/hwdb.bin /mnt/gentoo/usr/lib/udev/
 fi
 
+gccver=$(qlist -I -F '%{PV}' cross-${target}/gcc | sed 's/[^0-9].*//')
+for lib in \
+    libstdc++ \
+    libgcc_s \
+; do
+    cp /usr/lib/gcc/${target}/${gccver}/${lib}.so.* /mnt/gentoo/usr/lib64/
+done
+
 qemu-${target%%-*} \
 /mnt/gentoo/usr/sbin/ldconfig \
     -r /mnt/gentoo \
     -f /mnt/gentoo/etc/ld.so.conf
 
+if [ -d /mnt/gentoo/lib64/security ]; then
+    mv /mnt/gentoo/lib64/security/pam_*.so /mnt/gentoo/lib/security/
+fi
+
 rm -f /mnt/gentoo/lib/tmpfiles.d/provision.conf
 systemd-tmpfiles --root=/mnt/gentoo -E --exclude-prefix=/var --create