exp/vulncheck: make checks.bash work on Darwin
exp/vulncheck: make checks.bash work on Darwin

Fixes golang/go#51664

Change-Id: I03235cad0de24f825de2810d8f70336b12901d08
Reviewed-on: https://go-review.googlesource.com/c/exp/+/392594
Trust: Jonathan Amsterdam <e3d3698b2ccd5955e4adf250d0785062d0f9018b@google.com>
Run-TryBot: Jonathan Amsterdam <e3d3698b2ccd5955e4adf250d0785062d0f9018b@google.com>
Reviewed-by: Heschi Kreinick <e89ab2b172855aa0ad01c40c4d8a3535a61ac68a@google.com>

golang/exp,golang/exp,golang/exp