When building against eglibc, libc doesn't include librt therefore it must be explicitly included.
Signed-off-by: Philip Prindeville <philipp@redfish-solutions.com>
git-svn-id: svn://svn.openwrt.org/openwrt/packages@33467 3c298f89-4303-0410-b956-a3cf2f4a3e73