clarify config of pthread_workqueue vs. internal_workqueue

As suggested in review of PR-206, DISPATCH_USE_INTERNAL_WORKQUEUES
should not enable HAVE_PTHREAD_WORKQUEUES.  Instead, a new
DISPATCH_USE_WORKQUEUES is defined in queue.c to guard code that
should be enabled in either case.

Signed-off-by: Daniel A. Steffen <dsteffen@apple.com>
4 files changed