all: use t.TempDir in tests

This removes all usage of ioutil.TempDir in tests (and a few cases of
os.TempDir as well, while we're at it), which simplifies test cleanup a
lot.

Compile tested (go test -c) for most platforms (except zos).

Change-Id: I9178f5ec615c0a6cfef36e8de78c6b72e055b7cb
Reviewed-on: https://go-review.googlesource.com/c/sys/+/526297
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: qiulaidongfeng <2645477756@qq.com>
Auto-Submit: Ian Lance Taylor <iant@golang.org>

unix/getdirentries_test.go

@@ -30,11 +30,8 @@ func testGetdirentries(t *testing.T, count int) {
 	if count > 100 && testing.Short() && os.Getenv("GO_BUILDER_NAME") == "" {
 		t.Skip("skipping in -short mode")
 	}
-	d, err := ioutil.TempDir("", "getdirentries-test")
-	if err != nil {
-		t.Fatalf("Tempdir: %v", err)
-	}
-	defer os.RemoveAll(d)
+	d := t.TempDir()
+
 	var names []string
 	for i := 0; i < count; i++ {
 		names = append(names, fmt.Sprintf("file%03d", i))