cmd/asm: cryptic relocation errors with -spectre=all on GOARCH=386

[bcmills]

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

$ go version
go version devel go1.18-1cbec6851 Fri Oct 15 07:13:43 2021 +0000 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
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/usr/local/google/home/bcmills/.cache/go-build"
GOENV="/usr/local/google/home/bcmills/.config/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/tmp/tmp.6WLdHtHLTx/.gopath/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/tmp/tmp.6WLdHtHLTx/.gopath"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/google/home/bcmills/sdk/gotip"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/google/home/bcmills/sdk/gotip/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="devel go1.18-1cbec6851 Fri Oct 15 07:13:43 2021 +0000"
GCCGO="/usr/local/google/home/bcmills/bin/gccgo"
GOAMD64="v1"
AR="ar"
CC="gcc"
CXX="c++"
CGO_ENABLED="1"
GOMOD="/tmp/tmp.6WLdHtHLTx/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-build2894050865=/tmp/go-build -gno-record-gcc-switches"

What did you do?

$ GOARCH=386 go build -asmflags=all=-spectre=all .

-- go.mod --
module example

go 1.18
-- main.go --
package main

func main() {}

What did you expect to see?

Either a successful build, or an error message from cmd/asm indicating that -spectre=all is not supported on 386.

What did you see instead?

# example
gogo: relocation target runtime.retpolineBX not defined
runtime.rt0_go: relocation target runtime.retpolineAX not defined
runtime.mcall: relocation target runtime.retpolineAX not defined
runtime.mcall: relocation target runtime.retpolineDI not defined
runtime.systemstack: relocation target runtime.retpolineDI not defined
runtime.systemstack: relocation target runtime.retpolineAX not defined
runtime.asmcgocall: relocation target runtime.retpolineAX not defined
runtime.walltime: relocation target runtime.retpolineAX not defined
runtime.nanotime1: relocation target runtime.retpolineAX not defined
runtime.sigfwd: relocation target runtime.retpolineAX not defined
runtime.clone: relocation target runtime.retpolineSI not defined

This is distilled from a test failure seen in https://build.golang.org/log/446eb1e8cfb84ad3b91d8e92c2316ec2a3903562.

[gopherbot]

Change https://golang.org/cl/356190 mentions this issue: cmd/asm: report an error when trying to do spectre on 386