When running the build_farm on OS X xargs -i is an illegal option of xargs. Currently there is a test for this against freebsd but dosen't include the uname value of "Darwin"
Created attachment 2913 [details] buid_test.fns patch Add an addition test for uname = Darwin to declare XARGS_I="xargs -I '{}' -R -1"
Fixed in build farm svn.