We need to do that to pickup the prereq-build prepared symlinks for auxillary
operations like metadata scanning.

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@44378 3c298f89-4303-0410-b956-a3cf2f4a3e73