Ruby

Fix gc_verify_internal_consistency error for pattern_matching in ripper

gc_verify_internal_consistency reports "found internal inconsistency"
for "test_pattern_matching.rb".

http://ci.rvm.jp/results/trunk-gc-asserts@ruby-sp2-docker/4501173

Ruby's parser manages objects by two different ways.

1. For parser

• markable node holds objects
• call RB_OBJ_WRITTEN with p->ast as parent
• mark_ast_value marks objects

2. For ripper

• unmarkable node, NODE_RIPPER/NODE_CDECL, holds objects
• call rb_ast_add_mark_object. This function calls rb_hash_aset then
  RB_OBJ_WRITTEN is called with mark_hash as parent
• mark_hash marks objects

However in current pattern_matching implementation

• markable node holds objects
• call rb_ast_add_mark_object

This commit fix it to be #2.

This was inconsistency however always mark_hash is
made young by rb_ast_add_mark_object call then objects
are not collected.