merge revision(s) 50316: [Backport #11030]
* thread_pthread.c (reserve_stack): keep sp safe zone to get rid of crash by -fstack-check. [ruby-core:68740] [Bug #11030]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_1@50396 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
merge revision(s) 50316: [Backport #11030]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_1@50396 b2dd03c8-39d4-4d8f-98ff-823fe69b080e