Get threads working well on MacOS Arm64

- Now using 10x better GCD semaphores
- We now generate Linux-like thread ids
- We now use fast system clock / sleep libraries
- The APE M1 loader now generates Linux-like stacks

libc/runtime/enable_tls.c

@@ -190,7 +190,7 @@ textstartup void __enable_tls(void) {
   tib->tib_strace = __strace;
   tib->tib_ftrace = __ftrace;
   tib->tib_pthread = (pthread_t)&_pthread_main;
-  if (IsLinux()) {
+  if (IsLinux() || IsXnuSilicon()) {
     // gnu/systemd guarantees pid==tid for the main thread so we can
     // avoid issuing a superfluous system call at startup in program
     tid = __pid;