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/fmt/unuleb64.c

@@ -26,7 +26,7 @@
  * @param x receives number number
  * @return bytes decoded or -1 on error
  */
-int unuleb64(char *p, size_t n, uint64_t *x) {
+int unuleb64(const char *p, size_t n, uint64_t *x) {
   int k;
   size_t i;
   uint64_t t;