Fix r23638 "Convert Linkage to use MachineSignature." for crankshaft only architectures.

BUG=
R=paul.lind@imgtec.com, titzer@chromium.org

Review URL: https://codereview.chromium.org/538553002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23665 ce2b1a6d-e550-0410-aec6-3dcde31c8c00