Building pkg/rngd with latest alpine base fails on x86

[rn]

With linuxkit/alpine:96ad1eb5ec262b4cd0eef574cdc0b225b502d9ee, currently the latest alpine base image, building on x86 we get an error:

linuxkit pkg build .
Building "linuxkit/rngd:245d6e560556875e0b3e3e7ecfdd86f33e6be52f"
Pull (1 of 1): linuxkit/rngd:245d6e560556875e0b3e3e7ecfdd86f33e6be52f@sha256:f3837e2f7bbb4187b389d1b1b1b0621fe2da9977f485883e9b20ae71acf71b14
sha256:f3837e2f7bbb4187b389d1b1b1b0621fe2da9977f485883e9b20ae71acf71b14: Pulling from linuxkit/rngd
no matching manifest for linux/amd64 in the manifest list entries
No image pulled, continuing with build
Sending build context to Docker daemon  4.291MB
Step 1/13 : FROM linuxkit/alpine@sha256:187a64e2608be2c836486fe0772b4849720534e83021d0b06447538e0c5838b4 AS mirror
 ---> 7b9c7ac9c061
Step 2/13 : RUN apk add --no-cache go gcc musl-dev linux-headers
 ---> Using cache
 ---> ebea81500a00
Step 3/13 : ENV GOPATH=/go PATH=$PATH:/go/bin
 ---> Using cache
 ---> 3858b30d7e81
Step 4/13 : COPY cmd/rngd/ /go/src/rngd/
 ---> Using cache
 ---> 49003a184a05
Step 5/13 : RUN REQUIRE_CGO=1 go-compile.sh /go/src/rngd
 ---> Running in a5490145b803
gofmt...
govet...
golint...
ineffassign...
go test...
go build rngd: invalid flag in #cgo CFLAGS: -mrdrnd
The command '/bin/sh -c REQUIRE_CGO=1 go-compile.sh /go/src/rngd' returned a non-zero code: 1
exit status 1

the gcc --target-help lists -mrdrnd as an option

  -mrdrnd                     Support RDRND built-in functions and code generation.
  -mrdseed                    Support RDSEED instruction.

[rn]

ah, golang/go#23672 limits the flags one can use with cgo