eval.c: copy before cause setup
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58381 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
eval.c: copy before cause setup
up a cause not only a backtrace.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58381 b2dd03c8-39d4-4d8f-98ff-823fe69b080e