date_core.c: typed data

* ext/date/date_core.c (d_lite_type): turn into typed data.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47732 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
date_core.c: write-barrier

* ext/date/date_core.c (d_lite_type): add write-barrier.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47733 b2dd03c8-39d4-4d8f-98ff-823fe69b080e