x/sys/cpu: fails to build because `cacheLineSize redeclared in this block`

[Denton-L]

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

$ go version
go version go1.10.4 linux/amd64

Does this issue reproduce with the latest release?

Yes.

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

go env Output

$ go env
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/denton/.cache/go-build"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/denton/go"
GORACE=""
GOROOT="/usr/lib/go-1.10"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/go-1.10/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
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-build043849175=/tmp/go-build -gno-record-gcc-switches"

### What did you do?

I tried to compile the following:

package main

import _ "golang.org/x/sys/cpu"

func main() {}

What did you expect to see?

The compile should be successful.

What did you see instead?

$ go build
# golang.org/x/sys/cpu
../go/src/golang.org/x/sys/cpu/cpu_x86.go:9:23: cacheLineSize redeclared in this block
	previous declaration at ../go/src/golang.org/x/sys/cpu/cpu_wasm.go:11:23

[Denton-L]

Duplicated by #30668.