plugin: can't use plugin package in linkobj builds #33820
Description
What version of Go are you using (go version)?
$ go1.13rc1 version go version go1.13rc1 darwin/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="/Users/steeve/Library/Caches/go-build" GOENV="/Users/steeve/Library/Application Support/go/env" GOEXE="" GOFLAGS="" GOHOSTARCH="amd64" GOHOSTOS="darwin" GONOPROXY="" GONOSUMDB="" GOOS="darwin" GOPATH="/Users/steeve/go" GOPRIVATE="" GOPROXY="https://proxy.golang.org,direct" GOROOT="/Users/steeve/sdk/go1.13rc1" GOSUMDB="sum.golang.org" GOTMPDIR="" GOTOOLDIR="/Users/steeve/sdk/go1.13rc1/pkg/tool/darwin_amd64" GCCGO="gccgo" AR="ar" CC="clang" CXX="clang++" CGO_ENABLED="1" GOMOD="/Users/steeve/hdrgenerator/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 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/bs/51dlb_nn5k35xq9qfsxv9wc00000gr/T/go-build596961202=/tmp/go-build -gno-record-gcc-switches -fno-common"
What did you do?
$ cat test.go
package main
import _ "plugin"
func main() {}
$ go1.13rc1 tool compile -pack -o test.a -linkobj test.link.a test.go
$ go1.13rc1 tool link -o test test.link.a
test.link.a: missing package data entry
# this couldn't work, but I tested it anyway
$ go1.13rc1 tool link -o test test.a
/Users/steeve/sdk/go1.13rc1/pkg/tool/darwin_amd64/link: test.a: not package main
What did you expect to see?
A successful link.
What did you see instead?
test.link.a: missing package data entry
Related issue
Misc
It is also not possible to use buildmode=plugin in linkobj builds.