Skip back edge creation for "do ... while(false)" loops

Drive-by fix: Fix disassembling "prefetch" instruction on ia32

R=titzer@chromium.org

Review URL: https://codereview.chromium.org/131733002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18519 ce2b1a6d-e550-0410-aec6-3dcde31c8c00