Try to address the test timeouts on the solaris build bot.

We don't have efficient atomics on these platforms so we fall back
to explict locking.  Polling for values to change may prevent the
dependent from actually grabbing the lock and do something useful.

This is simply to get the tests to pass (and potentially identify
locking mistakes).  But we won't actually use named atomics on these
platforms in SVN.

* subversion/tests/libsvn_subr/named_atomic-test-common.h
  (watchdog_t): Add a flag to indicate the need to throttle polling.
  (init_watchdog): Init the new flag as well.
  (check_watchdog): Throttle execution when indicated.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1615369 13f79535-47bb-0310-9956-ffa450edef68
Follow-up on r1615369.

* subversion/tests/libsvn_subr/named_atomic-test-common.h
  (test_pipeline_loop): Skip watchdog and throttling when polling
                        was not necessary.  I.e. let the tokens be
                        passed on without delay.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1615371 13f79535-47bb-0310-9956-ffa450edef68