tests: use waitpid(..., WNOWAIT) to fix failing of main/fork under solaris

tests: use waitpid(..., WNOWAIT) to fix failing of main/fork under solaris

According to solaris docs:
  "One instance of a SIGCHLD signal is queued for each child process whose
  status has changed. If waitpid() returns because the status of a child
  process is available, and WNOWAIT was not specified in options, any pending
  SIGCHLD signal associated with the process ID of that child process is
  discarded. Any other pending SIGCHLD signals remain pending."

And interesting thing that it works if you add sleep(1) before waitpid(), and
also if you run with --verbose (some race or what).

But linux doesn't support WNOWAIT in waitpid() so add detection into
cmake/autotools.

Fixes: #387
Link: https://bugzilla.redhat.com/show_bug.cgi?id=840782