musl commit b64539ae06aa91a407359238f4e909adb9bfab3d fixed some octal
printing corner cases. I've written some tests to cover the affected
functionality to go in libc-test. I just added them to the existing
snprintf test rather than as a regression test since, despite it being
a bug fix, these fit the general form and I think it makes sense to
have them all in one place.

Rich