[oe] [for-krogoth] Fix build error in some hosts

[Otavio Salvador]

Hello,

There are two fixes for rrdtool which are simple and improve the
stability of it on some hosts. Those are:

daf619e rrdtool: only unset PERLHOSTLIB in do_configure
be3d4c0 rrdtool: fix do_configure failure on some hosts

Could those be queued for stable?

-- 
Otavio Salvador                             O.S. Systems
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