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/intrin/describesockoptname.c

@@ -26,8 +26,8 @@
  * Describes setsockopt() optname arguments.
  */
 const char *(DescribeSockOptname)(char buf[32], int l, int x) {
-  int i;
-  char *s, *p;
+  char *p;
+  const char *s;
   const struct MagnumStr *ms;
   p = buf;
   if (x) {