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/cmpxchg16b.internal.h

@@ -0,0 +1,46 @@
+#ifndef COSMOPOLITAN_LIBC_BITS_CMPXCHG16B_INTERNAL_H_
+#define COSMOPOLITAN_LIBC_BITS_CMPXCHG16B_INTERNAL_H_
+#include "libc/bits/asmflag.h"
+#if !(__ASSEMBLER__ + __LINKER__ + 0)
+COSMOPOLITAN_C_START_
+
+/**
+ * Compares and exchanges 128-bit value, i.e.
+ *
+ *     if (*IfThing == *IsEqualToMe) {
+ *       *IfThing = ReplaceItWithMe;
+ *       return true;
+ *     } else {
+ *       *IsEqualToMe = *IfThing;
+ *       return false;
+ *     }
+ *
+ * Please note that Intel Architecture doesn't guarantee 16-byte memory
+ * accesses to be atomic on their own. Therefore _lockcmpxchg16b should
+ * be considered instead for both thread and asynchronous signal safety
+ *
+ * @param IfThing should point to aligned memory
+ * @param IsEqualToMe should point to in/out local variable
+ * @param ReplaceItWithMe might become the new memory value
+ * @return true if *IfThing was changed
+ */
+static inline bool _cmpxchg16b(uint128_t *IfThing, uint128_t *IsEqualToMe,
+                               uint128_t ReplaceItWithMe) {
+  bool DidIt;
+  uint64_t ax, bx, cx, dx;
+  ax = *IsEqualToMe;
+  dx = *IsEqualToMe >> 64;
+  bx = ReplaceItWithMe;
+  cx = ReplaceItWithMe >> 64;
+  asm volatile(ZFLAG_ASM("cmpxchg16b\t%1")
+               : ZFLAG_CONSTRAINT(DidIt), "+m"(*IfThing), "+a"(ax), "+d"(dx)
+               : "b"(bx), "c"(cx));
+  if (!DidIt) {
+    *IsEqualToMe = ax | (uint128_t)dx << 64;
+  }
+  return DidIt;
+}
+
+COSMOPOLITAN_C_END_
+#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
+#endif /* COSMOPOLITAN_LIBC_BITS_CMPXCHG16B_INTERNAL_H_ */