runtime: set GODEBUG=asyncpreemptoff=1 in TestCrashDumpsAllThreads

Fixes #35356

Change-Id: I67b9e57b88d00ed98cbc3aa0aeb26b5f2d75a3f7
Reviewed-on: https://go-review.googlesource.com/c/go/+/205720
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

src/runtime/crash_unix_test.go

@@ -15,7 +15,6 @@ import (
 	"os/exec"
 	"path/filepath"
 	"runtime"
-	"strings"
 	"sync"
 	"syscall"
 	"testing"
@@ -99,18 +98,17 @@ func TestCrashDumpsAllThreads(t *testing.T) {
 
 	cmd = exec.Command(filepath.Join(dir, "a.exe"))
 	cmd = testenv.CleanCmdEnv(cmd)
-	cmd.Env = append(cmd.Env, "GOTRACEBACK=crash")
-
+	cmd.Env = append(cmd.Env,
+		"GOTRACEBACK=crash",
 		// Set GOGC=off. Because of golang.org/issue/10958, the tight
 		// loops in the test program are not preemptible. If GC kicks
 		// in, it may lock up and prevent main from saying it's ready.
-	newEnv := []string{}
-	for _, s := range cmd.Env {
-		if !strings.HasPrefix(s, "GOGC=") {
-			newEnv = append(newEnv, s)
-		}
-	}
-	cmd.Env = append(newEnv, "GOGC=off")
+		"GOGC=off",
+		// Set GODEBUG=asyncpreemptoff=1. If a thread is preempted
+		// when it receives SIGQUIT, it won't show the expected
+		// stack trace. See issue 35356.
+		"GODEBUG=asyncpreemptoff=1",
+	)
 
 	var outbuf bytes.Buffer
 	cmd.Stdout = &outbuf