[turbofan] Save OOL constant pool pointer in CodeGenerator::AssemblePrologue.

BUG=
R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/541733002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23843 ce2b1a6d-e550-0410-aec6-3dcde31c8c00