A description of how to build EROS under FreeBSD, including a link to a set of prebuilt cross tools, can now be found in the 0.8 release notes at
http://www.cis.upenn.edu/~eros/project/release-notes.html
If you have already downloaded the main packages, you can get the updates patched into your current tree by doing
cd eros/src make quiet-update
shap