In addition to detect dead canary, we try to detect the very moment
when we smash the stack top.  Requested by k0kubun:
https://twitter.com/k0kubun/status/1085180749899194368


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66981 b2dd03c8-39d4-4d8f-98ff-823fe69b080e