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/mmap_zos_test.go

@@ -21,14 +21,16 @@ import (
 )
 
 func TestMmap(t *testing.T) {
-	tmpdir := mktmpdir(t)
-	filename := filepath.Join(filepath.Join(tmpdir, "testdata"), "memmapped_file")
+	tmpdir := filepath.Join(t.TempDir(), "testdata")
+	if err := os.Mkdir(tmpdir, 0700); err != nil {
+		t.Fatal(err)
+	}
+	filename := filepath.Join(tmpdir, "memmapped_file")
 	destination, err := os.Create(filename)
 	if err != nil {
 		t.Fatal("os.Create:", err)
 		return
 	}
-	defer os.RemoveAll(tmpdir)
 
 	fmt.Fprintf(destination, "%s\n", "0 <- Flipped between 0 and 1 when test runs successfully")
 	fmt.Fprintf(destination, "%s\n", "//Do not change contents - mmap test relies on this")
@@ -73,15 +75,3 @@ func TestMmap(t *testing.T) {
 		t.Fatalf("Munmap: %v", err)
 	}
 }
-
-func mktmpdir(t *testing.T) string {
-	tmpdir, err := ioutil.TempDir("", "memmapped_file")
-	if err != nil {
-		t.Fatal("mktmpdir:", err)
-	}
-	if err := os.Mkdir(filepath.Join(tmpdir, "testdata"), 0700); err != nil {
-		os.RemoveAll(tmpdir)
-		t.Fatal("mktmpdir:", err)
-	}
-	return tmpdir
-}