Add set_system_proxy for linux and android

common/settings/command.go

@@ -0,0 +1,19 @@
+package settings
+
+import (
+	"os"
+	"os/exec"
+	"strings"
+
+	"github.com/sagernet/sing-box/log"
+)
+
+func runCommand(name string, args ...string) error {
+	log.Debug(name, " ", strings.Join(args, " "))
+	command := exec.Command(name, args...)
+	command.Env = os.Environ()
+	command.Stdin = os.Stdin
+	command.Stdout = os.Stderr
+	command.Stderr = os.Stderr
+	return command.Run()
+}