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/rand/rand.h

@@ -17,7 +17,6 @@ void rt_end(double *, double *, double *, double *, double *);
 char *strfry(char *);
 int getentropy(void *, size_t);
 ssize_t getrandom(void *, size_t, unsigned);
-float randf(void);
 char *initstate(unsigned, char *, size_t);
 char *setstate(char *);
 long random(void);