It fails because the desktop icons *.desktop are not copied to %{buildroot}.

By looking at aranym.spec:
https://sourceforge.net/p/aranym/code/ci/master/tree/aranym.spec

I see that there are special cases for various OSes, but Mageia is not supported. So special cases should be added for Mageia. I suppose that Mageia is similar to Mandriva.

I also see:

# if present, use %distversion to find out which Mandriva version is being built
# define %distversion and %_icondir in your .rpmmacros if build fails

So a solution is probably to add %distversion and %_icondir in the builer's .rpmmacros, but I don't know what to put there. Probably the same as Mandriva.

Quick test: you could add the following line at the top of aranym.spec to see if it does the trick:
%define mandriva_version mageia

References:
French Mageia forum: http://www.mageialinux-online.org/forum/topic-15485+rpmbuild-aranym.php
Official Mageia RPM spec: http://svnweb.mageia.org/packages/cauldron/aranym/current/SPECS/aranym.spec?revision=442179&view=markup