local: encode invalid UTF-8 on macOS

backend/local/encode_darwin.go

@@ -0,0 +1,9 @@
+//+build darwin
+
+package local
+
+import (
+	"github.com/rclone/rclone/fs/encodings"
+)
+
+const enc = encodings.LocalMacOS

backend/local/encode_other.go

@@ -1,4 +1,4 @@
-//+build !windows
+//+build !windows,!darwin
 
 package local