For tests (in another repo) that use cgo, we'd like to set CGO_ENABLED=1
explicitly when evaluating cross-compiled deps with "go list".
Updates tailscale/corp#26717
Updates tailscale/corp#26737
Change-Id: Ic21a54379ae91688d2456985068a47e73d04a645
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>