grit: count/newgrd/unit: sanity check the command line

Unlike the other grit tools, these three weren't really checking the
command line options that closely.  Formalize it a bit so we reject
all unknown options and too few/many arguments.

Change-Id: Ifdd58be1b723ca8b09d5add0c3dcde7243a07ecc
Reviewed-on: https://chromium-review.googlesource.com/c/1338469
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608681}
3 files changed