Fix warnings

This change fixes Cosmopolitan so it has fewer opinions about compiler
warnings. The whole repository had to be cleaned up to be buildable in
-Werror -Wall mode. This lets us benefit from things like strict const
checking. Some actual bugs might have been caught too.

third_party/python/Objects/object.c

@@ -464,6 +464,7 @@ int
 _PyObject_IsFreed(PyObject *op)
 {
     uintptr_t ptr = (uintptr_t)op;
+    (void)ptr;
     if (_PyMem_IsFreed(&ptr, sizeof(ptr))) {
         return 1;
     }