cmd/go: don't pass -test.testlogfile on NaCl

It causes every test to fail as the log file is on the local file system,
not the NaCl file system.

Updates #22593

Change-Id: Iee3d8307317bd792c9c701baa962ebbbfa34c147
Reviewed-on: https://go-review.googlesource.com/83256
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/go/internal/test/test.go

@@ -1266,7 +1266,7 @@ func (c *runCache) builderRunTest(b *work.Builder, a *work.Action) error {
 	}
 
 	testlogArg := []string{}
-	if !c.disableCache {
+	if !c.disableCache && cfg.Goos != "nacl" {
 		testlogArg = []string{"-test.testlogfile=" + a.Objdir + "testlog.txt"}
 	}
 	args := str.StringList(work.FindExecCmd(), a.Deps[0].Target, testlogArg, testArgs)

src/cmd/go/testdata/src/testcache/script.sh

+#!/bin/sh
+exit 0