vm_eval.c: UncaughtThrowError

* vm_eval.c (rb_throw_obj): throw UncaughtThrowError instead of
  ArgumentError.  [Feature #10480]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48433 b2dd03c8-39d4-4d8f-98ff-823fe69b080e