[sift] add missing -lrt in CMakeLists.txt
[sift] add missing -lrt in CMakeLists.txt

jmichel-otb/s2p,MISS3D/s2p,MISS3D/s2p,mnhrdt/s2p,dyoussef/s2p,dyoussef/s2p,MISS3D/s2p,dyoussef/s2p,jmichel-otb/s2p,mnhrdt/s2p,carlodef/s2p,jmichel-otb/s2p,MISS3D/s2p,dyoussef/s2p,carlodef/s2p,jmichel-otb/s2p