* vm_trace.c: `TracePoint#enable(target_line:)` is supported.
  This option enables a hook only at specified target_line.
  target_line should be combination with target and :line event.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66008 b2dd03c8-39d4-4d8f-98ff-823fe69b080e