Bug #23294: Detection of sem_xxx functions on NetBSD broken and \ 	DragonflyBSD misc patches
Bug #23294: Detection of sem_xxx functions on NetBSD broken and \
	DragonflyBSD misc patches

Add the original intended test, since our current test for sched_yield
is insufficient to copy.


configure.in:
  We can't check for sched_yield, as that is in libc on FBSD.
  
  Re-add the check for sem_init in librt.

flynn1973/mariadb-aix,natsys/mariadb_10.2,davidl-zend/zenddbi,flynn1973/mariadb-aix,ollie314/server,flynn1973/mariadb-aix,davidl-zend/zenddbi,flynn1973/mariadb-aix,davidl-zend/zenddbi,ollie314/server,davidl-zend/zenddbi,natsys/mariadb_10.2,ollie314/server,natsys/mariadb_10.2,davidl-zend/zenddbi,ollie314/server,ollie314/server,ollie314/server,ollie314/server,natsys/mariadb_10.2,flynn1973/mariadb-aix,flynn1973/mariadb-aix,natsys/mariadb_10.2,flynn1973/mariadb-aix,davidl-zend/zenddbi,flynn1973/mariadb-aix,ollie314/server,natsys/mariadb_10.2,natsys/mariadb_10.2,davidl-zend/zenddbi,davidl-zend/zenddbi,ollie314/server,flynn1973/mariadb-aix,davidl-zend/zenddbi,natsys/mariadb_10.2,ollie314/server,flynn1973/mariadb-aix,natsys/mariadb_10.2,natsys/mariadb_10.2,davidl-zend/zenddbi,davidl-zend/zenddbi,slanterns/server,flynn1973/mariadb-aix,natsys/mariadb_10.2,ollie314/server