net/internal/cgotest: don't try to use cgo with netgo build tag
When using bazel with hermetic_cc_toolchain resolv.h is not available.
Change-Id: I2aed72e6c14535cb1400b30d285bf05aa2498fde
GitHub-Last-Rev:
818c72323d3c61576d61dbe7564d15cf866ed67e
GitHub-Pull-Request: golang/go#70141
Reviewed-on: https://go-review.googlesource.com/c/go/+/623816
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Mateusz Poliwczak <mpoliwczak34@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: David Chase <drchase@google.com>