Without this change, V8 won't build on RHEL/CentOS 6 because the distro
python is too old to know about the argparse module.

Can this commit be cherry-picked to the 4.4 branch?  It should apply
cleanly.

BUG=

Review URL: https://codereview.chromium.org/1192973004

Cr-Commit-Position: refs/heads/master@{#29186}