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/x/xloadzd.c

@@ -17,8 +17,8 @@
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/assert.h"
-#include "libc/bits/bits.h"
 #include "libc/fmt/leb128.h"
+#include "libc/intrin/lockcmpxchg.h"
 #include "libc/nexgen32e/crc32.h"
 #include "libc/runtime/runtime.h"
 #include "libc/x/x.h"
@@ -69,7 +69,7 @@ void *xloadzd(bool *o, void **t, const void *p, size_t n, size_t m, size_t c,
   }
   free(q);
   assert(crc32_z(0, r, c * z) == s);
-  if (lockcmpxchg(t, 0, r)) {
+  if (_lockcmpxchg(t, 0, r)) {
     __cxa_atexit(free, r, 0);
   } else {
     free(q);