The fix is to make sure that pthread_yield is declared (http://man7.org/linux/man-pages/man3/pthread_yield.3.html) in src/opa/test/test_primitives.c. This may be otherwise missed if "make check" is not tested, because I did that with this build.
Anyways, I'll probably fix this in my OpenPA fork (https://github.com/jeffhammond/OpenPA) and hope that you all accept my patches in fifo order, starting with the C11 port :-)