vm_insnhelper.c: rb_get_kwargs

* vm_insnhelper.c (rb_get_kwargs): get keyword argument values from an
  option hash, not only checking keys.
* dir.c (dir_initialize): use rb_get_kwargs.
* gc.c (gc_start_internal): ditto.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44035 b2dd03c8-39d4-4d8f-98ff-823fe69b080e