exists in the same build directory.

This fixes the dependency ordering noticed when building with
make -j (multiple jobs). I tested with distcheck and AM_MAKEFLAGS=-j8
and also confirmed by vorner (who first reported build problem).
I will make an autobuild use this (but not too frequent).


git-svn-id: svn://bind10.isc.org/svn/bind10/trunk@2826 e5f2f494-b856-4b98-b285-d166d9295462