The \0 delimited string array that the browser sends doesn't have
the program name and the IRT only tokenizes that and forwards
it along. We need argv[0] to make the llvm CL parser happy
(used for -help message, etc).

Alternatively, we could have the IRT fill in a program name
so that the argv is a real argv. That will involve less copying since
the argv will be the right size to begin with, but prevents each app
from customizing its argv[0] =/

BUG= https://code.google.com/p/nativeclient/issues/detail?id=4091
TEST= manual for now (construct the sel_universal script to only pass
the "--build-atts" flag and see it exits without being swallowed,
or pass "-Ofoo" and see an error + exit)

R=mtrofin@chromium.org, stichnot@chromium.org

Review URL: https://codereview.chromium.org/1041843003