runtime/debuginfo: Build info for plan 9 binaries cannot be read due to missing a.out implementation

[oridb]

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

$ go version
2aa473cc54128c1498f80263763a2a876308e565

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/orib/lib/cache/go-build'
GOENV='/usr/orib/lib/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='plan9'
GOINSECURE=''
GOMODCACHE='/usr/orib/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='plan9'
GOPATH='/usr/orib/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/orib/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLDIR='/usr/orib/go/pkg/tool/plan9_amd64'
GOVCS=''
GOVERSION='VERS'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='6c'
CXX='g++'
CGO_ENABLED='0'
GOMOD='/dev/null'
GOWORK=''
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 -fno-caret-diagnostics -Qunused-arguments -Wl,--no-gc-sections -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build3108623332=/tmp/go-build -gno-record-gcc-switches'

There is a missing implementation to read the debug version out of a plan 9 binary, which causes reading the
build info from a binary to fail:

    --- FAIL: TestScript/mod_install_pkg_version (2.71s)
        script_test.go:272: 
            # (2022-07-17T01:37:54Z)
            # 'go install pkg@version' works outside a module. (1.106s)
            # 'go install pkg@version' reports an error if modules are disabled. (0.069s)
            # 'go install pkg@version' ignores go.mod in current directory. (1.326s)
            > cd m
            $WORK/gopath/src/m
            > cp go.mod go.mod.orig
            > ! go list -m all
            [stderr]
            go: example.com/cmd@v1.1.0-doesnotexist: reading http://127.0.0.1:58036/mod/example.com/cmd/@v/v1.1.0-doesnotexist.info: 404 Not Found
            	server response: 404 page not found
            go: example.com/cmd@v1.1.0-doesnotexist: missing go.sum entry; to add it:
            	go mod download example.com/cmd
            [exit status: 'go 705913: 1']
            > stderr '^go: example.com/cmd@v1.1.0-doesnotexist: missing go.sum entry; to add it:\n\tgo mod download example.com/cmd$'
            > go install example.com/cmd/a@latest
            > cmp go.mod go.mod.orig
            > exists $GOPATH/bin/a$GOEXE
            > go version -m $GOPATH/bin/a$GOEXE
            [stderr]
            $WORK/gopath/bin/a: could not read Go build info from $WORK/gopath/bin/a: unrecognized file format
            > stdout '^\tmod\texample.com/cmd\tv1.0.0\t' # "latest", not from go.mod
            FAIL: testdata/script/mod_install_pkg_version.txt:24: no match for `(?m)^\tmod\texample.com/cmd\tv1.0.0\t` found in stdout

What did you see instead?

A test that passed after reading debug info.

[gopherbot]

Change https://go.dev/cl/418014 mentions this issue: debug/buildinfo: implement for Plan 9 a.out