merge revision(s) 44925: [Backport #9492]

	* configure.in: check if pthread_setname_np is available.

	* thread_pthread.c: pthread_setname_np is not available on old
	  Darwins.  [ruby-core:60524] [Bug #9492]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_1@45090 b2dd03c8-39d4-4d8f-98ff-823fe69b080e