thread_pthread.c: define attr only if used
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42731 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
thread_pthread.c: define attr only if used
used, and merge pthread_create() calls.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42731 b2dd03c8-39d4-4d8f-98ff-823fe69b080e