Calls use registers for target, new_target and argument count.
We don't always respect argument count. It didn't bite us in the past
because the code paths where we clobbered it never used it, though
in future it could be an issue.

BUG=
R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/1683593003

Cr-Commit-Position: refs/heads/master@{#33865}