Use weak cells in map checks in polymorphic ICs.

BUG=v8:3663
LOG=N

Review URL: https://codereview.chromium.org/753993003

Cr-Commit-Position: refs/heads/master@{#25581}
[x64] introduce vex prefix version of float64 arithmetic binop

BUG=
R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/764863002

Patch from Weiliang Lin <weiliang.lin@intel.com>.

Cr-Commit-Position: refs/heads/master@{#25582}