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.

libc/calls/gettimeofday.c

@@ -55,7 +55,6 @@ static gettimeofday_f *__gettimeofday = __gettimeofday_init;
  */
 int gettimeofday(struct timeval *tv, struct timezone *tz) {
   int rc;
-  axdx_t ad;
   if (IsAsan() && ((tv && !__asan_is_valid(tv, sizeof(*tv))) ||
                    (tz && !__asan_is_valid(tz, sizeof(*tz))))) {
     rc = efault();