cmd/go: TestDocsUpToDate is incompatible with android emu builder environment

[dmitshur]

CL 468636 (CC @bcmills) recently improved TestDocsUpToDate to invoke go help documentation directly, without the mkalldocs.sh script, but it's not able to run at least in the emu android builders, failing with:

--- FAIL: TestDocsUpToDate (0.00s)
    help_test.go:34:  help documentation: exec: no command
FAIL
exitcode=1
FAIL	cmd/go	0.550s

(https://build.golang.org/log/3cee601aeb5302bcf6b0304d14ef713c9f3bff76)

CC @golang/android.

[dmitshur]

The problem seems to be that testGo is only set when testenv.HasGoBuild() reports positively, but when GOOS=android it returns false. The test currently doesn't check testenv.HasGoBuild() nor testGo being non-empty.

[bcmills]

Agreed — I just noticed that too. Probably we should set testGo if testenv.HasExec is true, since not every Go command is go build.

Independently, I think there are some pretty deep problems with the way the go_android_exec wrapper is setting up the build environment. 😕

[gopherbot]

Change https://go.dev/cl/472095 mentions this issue: cmd/go: set up testGo if the test can exec at all