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/testlib/quota.c

@@ -46,7 +46,6 @@ static dontasan dontubsan relegated uint64_t CountMappedBytes(void) {
 }
 
 static relegated void DieBecauseOfQuota(int rc, const char *message) {
-  int e = errno;
   char hostname[32];
   stpcpy(hostname, "unknown");
   gethostname(hostname, sizeof(hostname));