vm_trace.c: isolate errinfo in trace blocks

* vm_trace.c (rb_threadptr_exec_event_hooks_orig): errinfo should not
  be propagated to trace blocks so that no argument raise does not
  throw internal objects.  [ruby-dev:47793] [Bug #9088]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43561 b2dd03c8-39d4-4d8f-98ff-823fe69b080e