rsync: use system zlib and popt, also do not lose debug options

rsync by default compiles statically its own zlib and popt
libraries, it is better to use system wide libraries instead -
both for disk and memory consumption. Change rsync package
accordingly.

Also previously a debug configure option has been lost, as
overwritten by '--with-included-popt' option - fixed.

For example, on ARMv5 rsync binary size is reduced by about 25%.

Signed-off-by: Denis Mingulov <denis@mingulov.com>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>