os: Work if "ffi" module is not available (provide wrappers for "uos").

os/os/__init__.py

@@ -31,6 +31,7 @@ environ = {"WARNING": "NOT_IMPLEMENTED"}
 
 libc = ffilib.libc()
 
+if libc:
     chdir_ = libc.func("i", "chdir", "s")
     mkdir_ = libc.func("i", "mkdir", "si")
     rename_ = libc.func("i", "rename", "ss")