Add a separate step to copy the scripts to the intermediate directory and
run them from there.

BUG=angleproject:583

Change-Id: I307a2810ac03c00248cba1f227f128a1517c6574
Reviewed-on: https://chromium-review.googlesource.com/193432Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shannon Woods <shannonwoods@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>