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

examples/forkrand.c

@@ -8,6 +8,7 @@
 ╚─────────────────────────────────────────────────────────────────*/
 #endif
 #include "libc/calls/calls.h"
+#include "libc/intrin/kprintf.h"
 #include "libc/log/check.h"
 #include "libc/log/log.h"
 #include "libc/nt/nt/process.h"