Add direct_dependent_settings for v8 dll so targets that depend on v8
has USING_V8_SHARED defined.

Review URL: http://codereview.chromium.org/2946014/show

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5099 ce2b1a6d-e550-0410-aec6-3dcde31c8c00