fix sem_close regression test
    
    sem_close with O_CREAT takes 4 parameters, not 3. The last parameter,
    the initial value for the semaphore, had an arbitrary value from
    whatever was on the stack, and lead to spurious failures with EINVAL
    when it happened to be greater than SEM_VALUE_MAX. Since there isn't
    error checking in this test, this lead to a segfault in the first
    sem_post call.