cgo: missing format directive in error message

[kr]

Please answer these questions before submitting your issue. Thanks!

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

go version go1.6.1 linux/amd64

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

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH=""
GORACE=""
GOROOT="/usr/local/go"
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GO15VENDOREXPERIMENT="1"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0"
CXX="g++"
CGO_ENABLED="1"

1. What did you do?
   If possible, provide a recipe for reproducing the error.
   A complete runnable program is good.
   A link on play.golang.org is best.

try to build this file

package x

import "C"

func init() {
    println(C.enum_Foo.bar)
}

1. What did you expect to see?

./a.go:6:10: only C variables allowed in selector expression: enum_Foo

1. What did you see instead?

./a.go:6:10: only C variables allowed in selector expression%!(EXTRA string=enum_Foo)

[gopherbot]

CL https://golang.org/cl/22100 mentions this issue.