fix.
It uses a InstallDev/Post hook to find all .la files which are going to be
installed in the staging dir and prefixes every path in those files which starts
with /usr/lib with $(STAGING_DIR).
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@12586 3c298f89-4303-0410-b956-a3cf2f4a3e73