+dnl tests:
+dnl pthread_yield() was renamed to sched_yield() in Draft 10, so
+dnl only a Draft 10 library will define this
+dnl PTHREAD_INTR_ENABLE was introduced in Draft 6, and renamed to
+dnl PTHREAD_CANCEL_ENABLE in Draft 7. Draft 7-10 has _CANCEL_,
+dnl only Draft 6 has _INTR_
+dnl PTHREAD_MUTEX_INITIALIZER was introduced in Draft 5. It's not
+dnl interesting to us because we don't try to statically
+dnl initialize mutexes. 5-10 has it.
+dnl pthread_attr_create was renamed to pthread_attr_init after Draft 4.
+dnl Draft 6-10 has _init, Draft 4 has _create. (dunno about 5)
+dnl
+dnl Besides the use of sched_yield vs pthread_yield, differences from
+dnl Draft 7 thru Draft 10 don't appear significant for our purposes.
+dnl