os: add Args and stub it with mock data

src/runtime/runtime.go

@@ -24,9 +24,12 @@ func GOROOT() string {
 	return "/usr/local/go"
 }
 
+// TODO: fill with real args.
+var args = []string{"/proc/self/exe"}
+
 //go:linkname os_runtime_args os.runtime_args
 func os_runtime_args() []string {
-	return nil
+	return args
 }
 
 // Copy size bytes from src to dst. The memory areas must not overlap.