Revert "Make it possible to compile d8 for the host toolset as well" and "For V8, only build d8 on target"

This reverts commits r18618 and r18619 for breaking arm compilation.

BUG=
TBR=jochen@chromium.org

Review URL: https://codereview.chromium.org/139273004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18620 ce2b1a6d-e550-0410-aec6-3dcde31c8c00