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

libc/intrin/kprintf.h

@@ -5,6 +5,7 @@ COSMOPOLITAN_C_START_
 
 void kprintf(const char *, ...);
 size_t ksnprintf(char *, size_t, const char *, ...);
+size_t kusnprintf(char *, size_t, const char *, ...);
 void kvprintf(const char *, va_list);
 size_t kvsnprintf(char *, size_t, const char *, va_list);
 bool kisdangerous(const void *);