objspace.c: use rb_ident_hash_new
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@51515 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
objspace.c: use rb_ident_hash_new
rb_ident_hash_new instead of funcall Hash#compare_by_id.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@51515 b2dd03c8-39d4-4d8f-98ff-823fe69b080e