* thread_win32.h (rb_thread_lock_t): make a union for USE_WIN32_MUTEX.
  this internal is used only in thread_win32.c, but has to be complete
  to define rb_thread_t.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@36119 b2dd03c8-39d4-4d8f-98ff-823fe69b080e