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/signal_test.c

@@ -24,13 +24,12 @@
 #include "libc/sysv/consts/sig.h"
 #include "libc/testlib/testlib.h"
 
-testonly void OnCtrlC(int sig) {
+testonly void OnUsr1(int sig) {
   _exit(0);
 }
 
 TEST(signal, test) {
-  if (IsWindows()) return; /* omg */
-  ASSERT_NE(SIG_ERR, signal(SIGINT, OnCtrlC));
-  ASSERT_NE(-1, raise(SIGINT));
+  ASSERT_NE(SIG_ERR, signal(SIGUSR1, OnUsr1));
+  ASSERT_NE(-1, raise(SIGUSR1));
   __die();
 }