Plan 9 a.out was not implemented for debug/buildinfo, which
was causing test failures on Plan 9. This adds an implementation,
and causes the tests to pass.
Fixes #53949
Change-Id: I90a307ef9babf8cf381f8746d731cac2206b234a
Reviewed-on: https://go-review.googlesource.com/c/go/+/418014 Reviewed-by: Ian Lance Taylor <iant@google.com> Reviewed-by: Benny Siegert <bsiegert@gmail.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>