os: return proper user directories on iOS

Separating iOS into its own runtime constant broke the logic
here to derive the correct home, cache, and config directories
on iOS devices.

Fixes #42878

Change-Id: Ie4ff57895fcc34b0a9af45554ea3a346447d2e7a
GitHub-Last-Rev: 5e74e64
GitHub-Pull-Request: #42879
Reviewed-on: https://go-review.googlesource.com/c/go/+/273947
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Trust: Emmanuel Odeke <emmanuel@orijtech.com>

Author: whereswaldon

src/os/file.go

@@ -406,7 +406,7 @@ func UserCacheDir() (string, error) {
 			return "", errors.New("%LocalAppData% is not defined")
 		}
 
-	case "darwin":
+	case "darwin", "ios":
 		dir = Getenv("HOME")
 		if dir == "" {
 			return "", errors.New("$HOME is not defined")
@@ -457,7 +457,7 @@ func UserConfigDir() (string, error) {
 			return "", errors.New("%AppData% is not defined")
 		}
 
-	case "darwin":
+	case "darwin", "ios":
 		dir = Getenv("HOME")
 		if dir == "" {
 			return "", errors.New("$HOME is not defined")
@@ -505,10 +505,8 @@ func UserHomeDir() (string, error) {
 	switch runtime.GOOS {
 	case "android":
 		return "/sdcard", nil
-	case "darwin":
-		if runtime.GOARCH == "arm64" {
-			return "/", nil
-		}
+	case "ios":
+		return "/", nil
 	}
 	return "", errors.New(enverr + " is not defined")
 }