Implement os.RemoveAll()

TODO: enable test on windows once Readdir is implemented there

src/os/tempfile_test.go

@@ -2,6 +2,9 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build !baremetal && !js && !wasi
+// +build !baremetal,!js,!wasi
+
 package os_test
 
 import (