introduce GC_ASSERT().
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@59138 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
introduce GC_ASSERT().
vm_core.h but turn on by RGENGC_CHECK_MODE.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@59138 b2dd03c8-39d4-4d8f-98ff-823fe69b080e