rrdtool: adding the capability of native-builds to get rrdtool-oo in meta-cpan running

An additional layer for Perl modules from cpan (https://github.com/rehsack/meta-cpan

)
provides additional modules for dealing with rrd files: RRDTool::OO from Michael Schili.
This extension requires an executable version of rrdtool.

Signed-off-by: Jens Rehsack <sno@netbsd.org>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>