'inhibit_thread_createion' field.
* thread.c (rb_thread_terminate_all): set inhibit_thread_creation.
* thread.c (thread_s_new): don't permit to create new thread
  if the VM is under destruction. Otherwise evil finalizer code
  can make SEGV. [Bug #4992][ruby-core:37858]

* bootstraptest/test_objectspace.rb: new test for this fix.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@32492 b2dd03c8-39d4-4d8f-98ff-823fe69b080e