flag: exit 0 when -h or -help invoked but undefined
flag treats -h or -help as a special case to print a nice help
message, but exit with a status code of 2. This update makes
that status code 0.
Fixes #37533
Change-Id: I7e0bd29944ce46607fb7cfc6740734f7444a151a
GitHub-Last-Rev:
83f64d757bc3a9957c49caa5de74d05a96724771
GitHub-Pull-Request: golang/go#37530
Reviewed-on: https://go-review.googlesource.com/c/go/+/221427
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>