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/sock/kntwsadata.c

@@ -37,7 +37,7 @@
 struct NtWsaData kNtWsaData;
 
 static textwindows void WinSockCleanup(void) {
-  int i, rc;
+  int rc;
   (void)rc;
   rc = WSACleanup();
   NTTRACE("WSACleanup() → %d% lm", rc);