thread.c: fix deadlock
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39862 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
thread.c: fix deadlock
[ruby-dev:47182] [Bug #8137]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39862 b2dd03c8-39d4-4d8f-98ff-823fe69b080e