This change to run-perf.sh ensures that command line arguments are
prepended rather than appended to the passed in command. This is to
ensure that the arguments to d8 aren't accidentally passed through to
the js instead, as would be in the case:

tools/run-perf.sh d8 main.js -- --js-arg

A real-life example is passing --predictable to Octane's run.js

Review-Url: https://codereview.chromium.org/2391193003
Cr-Commit-Position: refs/heads/master@{#39999}