macho: fix tests
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 <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
Run-TryBot: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

golang/debug