The cross_build_gcc.sh script didn't set LINK, so cross builds would
fail at the last step.

BUG=
R=ulan@chromium.org

Review URL: https://codereview.chromium.org/170843011

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@19514 ce2b1a6d-e550-0410-aec6-3dcde31c8c00