The root filesystem on an Android device is "read-only", insofar that you cannot hang any files off the root tree and expect it to stay around. This is the same reason that you needed to extract the ramdisk and re-pack its contents in order to persist an init.rc change; any files you want to also locate at /
must be packed into the ramdisk as well. Android extracts root from the ramdisk on every boot.
A more conventional location for that file would be on the system partition, say in /system/lib