Fix d8 build error when V8_SHARED is unset on Linux.

TBR=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/21053002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15927 ce2b1a6d-e550-0410-aec6-3dcde31c8c00