Improve locks and signals

- Introduce fast spinlock API
- Double rand64() perf w/ spinlock
- Improve raise() on New Technology
- Support gettid() across platforms
- Implement SA_NODEFER on New Technology
- Move the lock intrinsics into LIBC_INTRIN
- Make SIGTRAP recoverable on New Technology
- Block SIGCHLD in wait4() on New Technology
- Add threading prototypes for XNU and FreeBSD
- Rewrite abort() fixing its minor bugs on XNU/NT
- Shave down a lot of the content in libc/bits/bits.h
- Let signal handlers modify CPU registers on New Technology

test/libc/calls/sigsuspend_test.c

@@ -46,10 +46,6 @@ void OnSigQueuing(int sig, siginfo_t *si, ucontext_t *ctx) {
 }
 
 TEST(sigsuspend, testSignalQueuingSelf) {
-  if (IsWindows()) {
-    // xxx: probably need a signal server to do this kind of signalling
-    return;
-  }
   sigset_t neu, old, bits;
   struct sigaction oldusr1, oldusr2;
   struct sigaction sa = {.sa_sigaction = OnSigQueuing, .sa_flags = SA_SIGINFO};