Since last jenkins restart, I've started getting "ln -s 2011-12-15_15-59-55 /usr/home/jenkins/jobs/Test/builds/1 failed: -1 " like messages in the log
Today I've tried to get into it.
It seems that JNA don't work, so LIBC don't work and PosixAPI is not native.
But in Java PosixAPI emulation, symlink creation fails with

java.lang.UnsupportedOperationException
at hudson.os.PosixAPI$1.getOutputStream(PosixAPI.java:66)
at org.jruby.ext.posix.util.ExecIt.runAndWait(ExecIt.java:47)

It looks to me impossible to create good implementation of PosixHandler with current singleton model as we need to specify working dir correctly for each call, so I've decided to simply skip PosixAPI in non-native mode, as it does pretty same as fallback code.
Here is commit I am going to test tomorrow that should fix the bug: https://github.com/tivv/jenkins/commit/5d1c149b6029d63596856b4457699b8362aefc20