The race detector is not fully functional on NetBSD yet. Without
this change, all.bash fails in TestOutput.

This unbreaks the netbsd-amd64 builder.

Update #26403
Fixes #27268

Change-Id: I2c7015692d3632aa1037f40155d4fc5c7bb1d8c3
Reviewed-on: https://go-review.googlesource.com/131555Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>