* gc.c (gc_mark_ptr): rename to gc_mark_set.
* gc.c (gc_mark): add gc_mark_ptr() to skip is_markable_object()
  check. gc_mark_maybe() can use gc_mark_ptr() directly because
  passed pointer is checked by is_pointer_to_heap().



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47532 b2dd03c8-39d4-4d8f-98ff-823fe69b080e