For the Om1 spec tests, we were generating commands like this:

  ./pydir/szbuild_spec2k.py -v -Om1 --target=x8632 -O2 --filetype=obj 253.perlbmk

where -Om1 and -O2 both appear.  Python's argparse allows an argument to be set multiple times, and the last one would win, i.e. -O2 is used instead of -Om1.

BUG= none
R=jpp@chromium.org

Review URL: https://codereview.chromium.org/1766603002 .