It adds a tiny bit of configuration to permit Sun Studio / suncc to successfully build the package. There is no code change, and no configuration change for the other platforms. Thanks for Brian Ripley for additional testing, and of course for running those build instances (and everything else he does) for the R project, and to Conrad Sanderson as upstream author of the Armadillo C++ library for linear algebra.
As usual, more information is on the RcppArmadillo page. Questions, comments etc should go to the rcpp-devel mailing list off the R-Forge page.