go.tools/importer: negate "cgo" build tag to avoid native code in "net".
go.tools/importer: negate "cgo" build tag to avoid native code in "net".

This removes the need for the caller to specify CGO_ENABLED=0
in the environment.

R=crawshaw
CC=golang-dev
https://golang.org/cl/13464045

emacsmirror/go-mode,dominikh/go-mode.el