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/runtime/clone.c

@@ -52,7 +52,7 @@
 #include "libc/thread/openbsd.internal.h"
 #include "libc/thread/thread.h"
 #include "libc/thread/tls.h"
-#include "libc/thread/tls2.h"
+#include "libc/thread/tls2.internal.h"
 #include "libc/thread/xnu.internal.h"
 
 #define kMaxThreadIds 32768
@@ -215,8 +215,6 @@ XnuThreadMain(void *pthread,                    // rdi
 
 static errno_t CloneXnu(int (*fn)(void *), char *stk, size_t stksz, int flags,
                         void *arg, void *tls, int *ptid, int *ctid) {
-  int rc;
-  bool failed;
   static bool once;
   struct CloneArgs *wt;
   if (!once) {