thread_pthread.c: cast to size_t
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44715 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
thread_pthread.c: cast to size_t
may be larger than size_t. [ruby-core:60113] [Bug #9454]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44715 b2dd03c8-39d4-4d8f-98ff-823fe69b080e