benchmark

compare_bench.py: fixup benchmark_options. (#435)

https://github.com/google/benchmark/commit/2373382284918fda13f726aefd6e2f700784797f
reworked parsing, and introduced a regression
in handling of the optional options that
should be passed to both of the benchmarks.

Now, unless the *first* optional argument starts with
'-', it would just complain about that argument:
	Unrecognized positional argument arguments: '['q']'
which is wrong. However if some dummy arg like '-q' was
passed first, it would then happily passthrough them all...

This commit fixes benchmark_options behavior, by
restoring original passthrough behavior for all
the optional positional arguments.