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.

test/libc/fmt/formathex64_test.c

@@ -22,7 +22,7 @@
 #include "libc/testlib/ezbench.h"
 #include "libc/testlib/testlib.h"
 
-char buf[19];
+char buf[100];
 
 void SetUp(void) {
   memset(buf, 0x55, sizeof(buf));