libssh2 upstream:
http://mirror.city-fan.org/ftp/contrib/yum-repo/rhel7/source/libssh2-1.9.0-2.0.cf.rhel7.src.rpm

reason for being in stackrpms:
needed to build FreeFileSync on EL derivatives because libcurl in distro is not as up-to-date as FreeFileSync upstream