thread_pthread.c: keep sp safe zone
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@50316 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
thread_pthread.c: keep sp safe zone
of crash by -fstack-check. [ruby-core:68740] [Bug #11030]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@50316 b2dd03c8-39d4-4d8f-98ff-823fe69b080e