build: make rclone build with wasip1/wasm as well as js/wasm

Fixes #7831

backend/protondrive/protondrive.go

@@ -1,3 +1,5 @@
+//go:build !wasm
+
 // Package protondrive implements the Proton Drive backend
 package protondrive
 

backend/protondrive/protondrive_test.go

@@ -1,3 +1,5 @@
+//go:build !wasm
+
 package protondrive_test
 
 import (

backend/protondrive/protondrive_unsupported.go

@@ -0,0 +1,7 @@
+// Build for sftp for unsupported platforms to stop go complaining
+// about "no buildable Go source files "
+
+//go:build wasm
+
+// Package protondrive implements the Proton Drive backend
+package protondrive