go: x/tools/cmd/gopls: errors reported in package with no errors

What version of Go are you using (go version)?

$ go version
go version go1.12.5 linux/amd64
$ go list -m golang.org/x/tools
golang.org/x/tools v0.0.0-20190524210228-3d17549cdc6b

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

$ go env
GOARCH="amd64"
GOBIN="/home/myitcv/gostuff/src/github.com/myitcv/govim/cmd/govim/.bin"
GOCACHE="/home/myitcv/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/myitcv/gostuff"
GOPROXY="https://proxy.golang.org/"
GORACE=""
GOROOT="/home/myitcv/gos"
GOTMPDIR=""
GOTOOLDIR="/home/myitcv/gos/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/myitcv/gostuff/src/github.com/myitcv/govim/go.mod"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build230798786=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Opened a file in Vim (using govim) that is part of a package that compiles and on which tests pass; received the following error message:

failed to run analyses for file:///home/myitcv/gostuff/src/github.com/myitcv/govim/cmd/govim/main.go: analysis skipped due to errors in package: [/home/myitcv/gos/src/net/lookup_unix.go:324:23: undeclared name: cgoLookupPTR /home/myitcv/gos/src/net/lookup_unix.go:124:24: undeclared name: cgoLooku
pCNAME /home/myitcv/gos/src/net/lookup_unix.go:108:23: undeclared name: cgoLookupPort /home/myitcv/gos/src/net/lookup_unix.go:96:24: undeclared name: cgoLookupIP /home/myitcv/gos/src/net/lookup_unix.go:81:24: undeclared name: cgoLookupHost]

This appears to have been introduced as part of https://go-review.googlesource.com/c/tools/+/178681

What did you expect to see?

No error message.

What did you see instead?

The above error message.

cc @stamblerre @ianthehat