macho: fix tests

Fix a few bugs that are causing the tests to fail.

Change-Id: Ie2d1b76ee4650a17092a0ff8aef004d118dabe84
Reviewed-on: https://go-review.googlesource.com/92419
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
1 file changed