thread_pthread.c: check stack on co-routine case
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@56060 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
thread_pthread.c: check stack on co-routine case
get_main_stack succeeded, on the "co-routine" case.
https://github.com/ruby/ruby/commit/53953ee#commitcomment-18887413
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@56060 b2dd03c8-39d4-4d8f-98ff-823fe69b080e