struct.c: use iseqval
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48754 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
struct.c: use iseqval
VALUE instead of rb_iseq_t to prevent from GC, as RB_GC_GUARD
makes sense only for local variables. [Feature #10575]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48754 b2dd03c8-39d4-4d8f-98ff-823fe69b080e