Fix EntryHookStub on ia32 and x64.

These stubs were computing the return address location incorrectly.
Add testing for same.

R=danno@chromium.org

Review URL: https://codereview.chromium.org/15769017

Patch from Sigurður Ásgeirsson <siggi@chromium.org>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14962 ce2b1a6d-e550-0410-aec6-3dcde31c8c00