unix: fix -d=checkptr slice failures on aix
unix: fix -d=checkptr slice failures on aix

Fix unsafe conversions to slices that are missing length or capacity.

Change-Id: I3a1f4d57e0884b647b4c3819ff014d09b87a1ce5
GitHub-Last-Rev: 9b6895a08d4d92fff16913c3d7b9495fecb741a1
GitHub-Pull-Request: golang/sys#66
Reviewed-on: https://go-review.googlesource.com/c/sys/+/225617
Run-TryBot: Tobias Klauser <0a68dd4915066ec5d3f81f75a828fee53dcc8822@gmail.com>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Tobias Klauser <0a68dd4915066ec5d3f81f75a828fee53dcc8822@gmail.com>
Trust: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

golang/sys,golang/sys,golang/sys