I've seen that one before and it seems to be safe to ignore it and continue with the build.
The closest I came to finding an answer on-line:
rt/tst-cpuclock2.out is a "timing" issue and can be ignored
the rest are due to building the test-suite with -Wl,--as-needed.
points to rt/tst-aio4.out, among a few others that might show up.
Hope this helps.