cmd/go: non-script staleness checks interact badly with GOFLAGS

[bcmills]

I think the non-script cmd/go tests are missing a step to zero out GOFLAGS from the user's environment.

The fix is probably to unset GOFLAGS in this block:

go/src/cmd/go/go_test.go

Lines 217 to 218 in 05ddb87

	// Don't let these environment variables confuse the test.
	os.Setenv("GOENV", "off")

~/go-review/src$ ./make.bash
Building Go cmd/dist using /usr/local/google/home/bcmills/go1.4. (go1.4-bootstrap-20170531 linux/amd64)
Building Go toolchain1 using /usr/local/google/home/bcmills/go1.4.
Building Go bootstrap cmd/go (go_bootstrap) using Go toolchain1.
Building Go toolchain2 using go_bootstrap and Go toolchain1.
Building Go toolchain3 using go_bootstrap and Go toolchain2.
Building packages and commands for linux/amd64.
---
Installed Go for linux/amd64 in /usr/local/google/home/bcmills/go-review
Installed commands in /usr/local/google/home/bcmills/go-review/bin

~/go-review/src$ go version
go version devel +edf60be151 Fri Dec 4 18:03:43 2020 +0000 linux/amd64

~/go-review/src$ export GOFLAGS='-gcflags=-e'

~/go-review/src$ go test cmd/go/...
go test proxy running at GOPROXY=http://127.0.0.1:34961/mod
--- FAIL: TestCacheListStale (0.29s)
    go_test.go:2271: running testgo [install p m]
    go_test.go:2272: running testgo [list -f={{.ImportPath}} {{.Stale}} m q p]
    go_test.go:2272: standard output:
    go_test.go:2272: m true
        q true
        p true

    go_test.go:2273: m should not be stale
    go_test.go:2273: pattern ^m false not found in standard output
--- FAIL: TestInstallDeps (0.33s)
    go_test.go:2528: running testgo [list -f={{.Target}} p1]
    go_test.go:2528: standard output:
    go_test.go:2528: /tmp/cmd-go-test-995578665/gotest858697184/pkg/linux_amd64/p1.a

    go_test.go:2530: running testgo [list -f={{.Target}} p2]
    go_test.go:2530: standard output:
    go_test.go:2530: /tmp/cmd-go-test-995578665/gotest858697184/pkg/linux_amd64/p2.a

    go_test.go:2532: running testgo [list -f={{.Target}} main1]
    go_test.go:2532: standard output:
    go_test.go:2532: /tmp/cmd-go-test-995578665/gotest858697184/bin/main1

    go_test.go:2535: running testgo [install main1]
    go_test.go:2541: running testgo [install p2]
    go_test.go:2546: running testgo [list -f {{.Stale}}:{{.StaleReason}} runtime]
    go_test.go:2546: standard output:
    go_test.go:2546: true:build ID mismatch

    go_test.go:2546: must be non-stale before install -i
--- FAIL: TestIssue22588 (0.12s)
    go_test.go:2306: running testgo [list -f={{.Stale}} runtime]
    go_test.go:2306: standard output:
    go_test.go:2306: true

    go_test.go:2307: running testgo [list -toolexec=/usr/bin/time -f={{.Stale}} runtime]
    go_test.go:2307: standard output:
    go_test.go:2307: true

    go_test.go:2308: incorrectly reported runtime as stale
    go_test.go:2308: pattern false not found in standard output
--- FAIL: TestGoTestDashIDashOWritesBinary (0.06s)
    go_test.go:1400: running testgo [list -f {{.Stale}}:{{.StaleReason}} runtime]
    go_test.go:1400: standard output:
    go_test.go:1400: true:build ID mismatch

    go_test.go:1400: must be non-stale before test -i
FAIL
FAIL    cmd/go  191.829s

CC @matloob @jayconrod

[gopherbot]

Change https://golang.org/cl/277453 mentions this issue: cmd/go: fix non-script staleness checks interacting badly with GOFLAGS