This adds an explicit {OsrPoll} bytecode into every loop header which
triggers on-stack replacement when armed. Note that each such bytecode
stores the static loop depths as an operand, and hence can be armed for
specific loop depths.

This also adds builtin code that triggers OSR compilation and switches
execution over to optimized code in case compilation succeeds. In case
compilation fails, the bytecode dispatch just continues unhindered.

R=rmcilroy@chromium.org
TEST=mjsunit/ignition/osr-from-bytecode
BUG=v8:4764

Review-Url: https://codereview.chromium.org/2172233002
Cr-Commit-Position: refs/heads/master@{#38043}